Light-emitting element, method for producing the same and display device

ABSTRACT

A light-emitting element of the present invention, includes: a porous light-emitting body including an insulator having a void and an inorganic phosphor particle; and at least two electrodes provided so as to contact with a surface of the light-emitting body. A voltage is applied to the at least two electrodes so as to generate discharge, and the light-emitting body is pumped by the discharge so as to emit light. Thereby, a light-emitting element that is reduced in a deterioration of brightness and a degradation of reliability of phosphors and does not require the vacuum encapsulation and the application of a high voltage, which are required for glow discharge, and still-higher level of thin-film technology can be provided. By arranging these light-emitting elements two-dimensionally in a matrix form, a flat display device with a simple configuration can be provided at a low cost.

TECHNICAL FIELD

The present invention relates to a light-emitting element, a method forproducing the same and a display device in which light-emitting elementsare arranged.

BACKGROUND ART

Recently, attention has been drawn to a flat-type display as a displaydevice, for example, a plasma display has been put into practical use.The plasma display has received attention because it permits upsizingeasily and allows high brightness and wide viewing-angle to be attained.However, since the configuration of the display is complicated and amanufacturing process thereof also is complicated, the cost of thecurrent display still remains high, although there has been improvement.

Furthermore, another display utilizing an electroluminescent (EL)phenomenon also has been proposed. In an inorganic EL, light is emittedby recombination of an electron of an inorganic phosphor with a hole orthe use of an exciton, which is caused by a voltage applied throughelectrodes arranged at an inorganic phosphor made of semiconductor, orlight is emitted when an atom or an ion serving as a luminescence centerthat is excited by a collision with of an accelerated electron in asemiconductor returns to the original state (Refer to “Optical PropertyHandbook”, SHIGEO Shiotani et al., published by Asakura shoten (1984),pp 523-531 and “Principles of Light-emission”, HIROSHI Kobayashi,published by Asakura Shoten (2000) pp 10 to 11). However, the inorganicEL has not been used widely yet because of reasons such as thedifficulty of upsizing and a high process cost due to the use of athin-film process. Although an organic dispersion EL also is proposed,it has the drawbacks of the difficulty in realizing full-color and aninsufficient life property. Therefore, this also has not been usedwidely.

As displays utilizing discharge other than the plasma display that hasbeen put into practical use, a proposed one is as described in JPH11(1999)-162640 A, such that, within an enclosing container, organicphosphor molecules are absorbed on at least a surface of porousparticles (metal oxides or high-polymer spherical particles), and apositive electrode and a negative electrode further are formed on asurface thereof. A DC electric field is applied to these electrodes soas to induce discharge, thus allowing light-emission. Furthermore, JPS59(1984)-18558 A proposes that light is emitted by using ultravioletrays generated by glow-discharge of a rare gas, such as He and Xe, in avacuum between electrodes arranged at phosphors.

The above light-emitting element described in JP H11(1999)-162640 A hasthe problems of a deterioration of brightness and a degradation ofreliability, which are due to vaporization (sublimation) of organicphosphor molecules caused by a voltage load or heat generated bydischarge.

Furthermore, in order to generate glow discharge, the inventiondescribed in JP S59(1984)-18558 A requires the application of a highvoltage and the vacuum encapsulation of a rare gas.

DISCLOSURE OF THE INVENTION

In view of the above-stated problems, the present invention provides alight-emitting element which has reduced deterioration of brightness anddegradation of reliability of phosphors and does not require the vacuumencapsulation and the application of a high voltage, which are requiredfor glow discharge, and still-higher level of thin-film technology, anda method for producing the same. The present invention further providesa display with a simple configuration and at a low cost.

The present invention is directed to a light-emitting element includinga porous light-emitting body including an insulator having a void and aninorganic phosphor particle; and at least two electrodes provided so asto contact with a surface of the light-emitting body. A voltage isapplied to the at least two electrodes so as to generate discharge, andthe light-emitting body is pumped by the discharge so as to emit light.

A display device of the present invention is obtained by arranging theabove-stated light-emitting elements in a matrix form.

A method for producing a light-emitting element of the present inventionis for producing the above-stated light-emitting element and includesthe steps of: a first step of applying an inorganic phosphor paste on asurface of a sheet-form porous body made up of the insulator having avoid; a second step of conducting a heat treatment for the insulator soas to form the porous light-emitting body; and a third step of formingthe at least two electrodes contacting with the surface of thelight-emitting body.

Another method for producing a light-emitting element of the presentinvention is for producing the above-stated light-emitting element andincludes the steps of: a first step of applying a paste containing aninsulative fiber and an inorganic phosphor particle on a conductivesubstrate and conducting a heat treatment so as to form the porouslight-emitting body, and a second step of forming the electrodes so asto contact with the surface of the light-emitting body.

Still another method for producing a light-emitting element of thepresent invention is for producing the above-stated light-emittingelement and includes the steps of: a first step of shaping a pastecontaining an insulative fiber and an inorganic phosphor particle andconducting a heat treatment so as to form the porous light-emittingbody, and a second step of forming the at least two electrodes so as tocontact with the surface of the light-emitting body.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a light-emitting element accordingto Embodiment 1 of the present invention.

FIG. 2A is a cross-sectional view of light-emitting particles ofEmbodiments 1 and 3 of the present invention, and FIG. 2B is across-sectional view of light-emitting particles of Embodiments 1 and 3of the present invention.

FIG. 3 is a cross-sectional view of a light-emitting element ofEmbodiment 2 of the present invention.

FIG. 4 is a cross-sectional view of a light-emitting element ofEmbodiment 3 of the present invention.

FIG. 5 is a cross-sectional view of a light-emitting element ofEmbodiment 4 of the present invention.

FIG. 6 is a cross-sectional view of a light-emitting element ofEmbodiment 5 of the present invention.

FIG. 7 is a cross-sectional view of a light-emitting element ofEmbodiment 7 of the present invention.

FIG. 8 is a cross-sectional view of a light-emitting element ofEmbodiment 8 of the present invention.

FIG. 9 is a cross-sectional view of a light-emitting element ofEmbodiment 9 of the present invention.

FIG. 10 is a cross-sectional view of a light-emitting element ofEmbodiment 10 of the present invention.

FIG. 11 is a cross-sectional view of a light-emitting element ofEmbodiment 11 of the present invention.

FIG. 12 is a cross-sectional view of a light-emitting element ofEmbodiment 12 of the present invention.

FIG. 13 is a cross-sectional view of a light-emitting element ofEmbodiment 13 of the present invention.

FIG. 14 is a cross-sectional view of a light-emitting element ofEmbodiment 14 of the present invention.

FIG. 15 is a cross-sectional view of a light-emitting element ofEmbodiment 15 of the present invention.

FIG. 16A is a cross-sectional view of the light-emitting element ofEmbodiment 7 of the present invention, which has a light-shielding filmformed from a surface side of the light-emitting body toward the insidethereof, and FIG. 16B is a cross-sectional view of the light-emittingelement having a groove.

BEST MODE FOR CARRYING OUT THE INVENTION

A light-emitting element of the present invention is a light-emittingelement including a porous light-emitting body on a surface of which aninsulative inorganic substance is formed and at least two electrodescontacting with a surface of the light-emitting body. A voltage isapplied to the light-emitting element so as to generate surface creepageat a surface of the light-emitting body and inside thereof, andultraviolet light generated by the surface creepage pumps thelight-emitting body so as to emit light.

Another light-emitting element of the present invention includes aporous light-emitting body including an assembly of inorganic phosphorparticles whose surfaces are coated with an insulative inorganicsubstance, and at least two electrodes contacting with a surface of thelight-emitting body. A voltage is applied to the light-emitting elementso as to generate surface creepage at a surface of the light-emittingbody and inside thereof, and, for example, ultraviolet light generatedby the surface creepage pumps the light-emitting body so as to emitlight.

Furthermore, as the insulative inorganic substance (insulative metaloxide), at least one substance selected from the group consisting ofY₂O₃, Li₂O, MgO, CaO, BaO, SrO, Al₂O₃, SiO₂, MgTiO₃, CaTiO₃, BaTiO₃,SrTiO₃, ZrO₂, TiO₂, B₂O₃, PbTiO₃, PbZrO₃ and PbZrTiO₃ (PZT) may be used.These materials are stable substances having considerably small standardfree energy of formation of oxides ΔG_(f) ⁰(e.g., −100 kcal/mol or lessat room temperatures) or are substances having a capacity of 100 or moreas a dielectric constant. Thus, they have a high insulation resistancevalue and facilitate the generation of the surface creepage, and canmaintain an insulative metal oxide property that tends not to be reducedeven when the surface creepage occurs.

Furthermore, the light-emitting element may be provided with a throughhole in the light-emitting body between the electrodes that is bored onpurpose using a needle or the like, which facilitates the generation ofthe surface creepage even at the inside of the light-emitting body.

Furthermore, in the light-emitting element, a substance with aresistance lower than that of an insulative metal oxide may be dispersedwithin the light-emitting body between the electrodes, which facilitatesthe generation of the surface creepage at the surface and even at theinside of the light-emitting body.

Furthermore, in the light-emitting element, an inside of thelight-emitting body may be filled with inert gas so as to form anatmosphere that facilitates the generation of ultraviolet light.

Another light-emitting element of the present invention includes: aporous light-emitting body including an insulator having a void and aninorganic phosphor particle; and at least two electrodes provided so asto contact with a surface of the light-emitting body. A voltage isapplied to the at least two electrodes so as to generate discharge, andultraviolet light generated by the discharge pumps the light-emittingbody so as to emit light.

The insulator having a void is at least one selected from a fibrousstructure and a foam having continuous bubbles. This configurationfacilitates the attachment of the inorganic phosphor particle and thedischarge. The insulator preferably is colorless or white, because thisdoes not pose any obstacles for making red, blue and green phosphorsemit light.

Furthermore, the light-emitting body preferably is one obtained byattaching the inorganic phosphor particle to a surface of the insulatorhaving a void.

Furthermore, preferably, the insulator fiber having a void is aninorganic substance that contains at least one type selected from thegroup consisting of Al, Si, Ca, Mg, Ti, Zn and B. These materials have ahigh insulation resistance value and have excellent heat-resistanceproperties and resistance to acids and alkalis. Therefore, in thelight-emitting element, the discharge becomes likely to occur and aconfiguration resistant to heat and chemicals can be obtained.

Furthermore, preferably, the fiber is one obtained by crushinginsulative ceramic or glass. They have a high insulation resistancevalue and have excellent heat-resistance properties and resistance toacids and alkalis, and therefore in the light-emitting element, thedischarge becomes likely to occur and a configuration resistant to heatand chemicals can be obtained.

Preferably, the fiber is a heat-resistant synthetic fiber with a heatdistortion temperature of 220° C. or more. The heat distortiontemperature refers to a temperature at which the fiber is not molten orsoftened. Since the fiber is just charged into the light-emitting body,it is sufficient for the fiber simply to hold its shape without beingmolten or softened. As examples of the heat-resistant synthetic fiberhaving a heat distortion temperature of 220° C. or more, well-knownheat-resistant fibers are available including: fluorine fibers such aspolytetrafluoroethylene (PTFE),tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA),polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF),polyvinyl fluoride (PVF), tetrafluoroethylene-hexafluoropropylenecopolymer (FEP) and tetrafluoroethylene-ethylene copolymer (PETFE);polyimide fiber, aramid fiber (including meta group and para group),polyester fiber, polyamide fiber, polyamideimide fiber, polyesterimidefiber, polyether fiber, polyetherether fiber and polysulfone fiber.

Furthermore, the inorganic phosphor particle may be covered with aninsulative inorganic substance, whereby the discharge can be generatedwith efficiency.

Furthermore, as the insulative inorganic substance, at least onesubstance selected from the group consisting of Y₂O₃, Li₂O, MgO, CaO,BaO, SrO, Al₂O₃, SiO₂, MgTiO₃, CaTiO₃, BaTiO₃, SrTiO₃, ZrO₂, TiO₂, B₂O₃,PbTiO₃, PbZrO₃ and PbZrTiO₃ (PZT) may be used. These materials arestable substances having considerably small standard free energy offormation of oxides AGF (e.g., −100 kcal/mol or less at roomtemperatures) or are substances having a capacity of 100 or more as adielectric constant. Thus, they have a high insulation resistance valueand facilitate the generation of the discharge, and are insulative metaloxides that tend not to be reduced even when the discharge occurs andhave excellent durability.

Furthermore, a substance with a resistance lower than that of theinsulative fiber may be dispersed within the light-emitting body betweenthe electrodes, which facilitates the generation of the discharge at asurface and even at the inside of the light-emitting body.

An inside of the light-emitting body may be an atmosphere at atmosphericpressure or may be filled with inert gas, which facilitates thegeneration of ultraviolet light.

Furthermore, assuming that a weight of the insulative fiber is 1, themixture may be conducted so that a weight of the inorganic phosphorparticle is within a range of 0.1 to 10.0. This facilitates thegeneration of the discharge at a surface and even at the inside of thelight-emitting body.

Furthermore, preferably, the insulative fiber has a diameter of 0.1 to20.0 μm and a length of 0.5 to 100 μm, and the inorganic phosphorparticle has an average particle diameter of 0.1 to 5.0 μm. Thisfacilitates the generation of the discharge at a surface and even at theinside of the light-emitting body.

Next, in the first method for producing a light-emitting element of thepresent invention, it is preferable that the inorganic phosphor pastecontains an inorganic phosphor particle whose surface is covered with aninsulative inorganic substance. According to this method, alight-emitting element having a configuration facilitating the efficientgeneration of the discharge can be produced.

Furthermore, the covering with the insulative inorganic substance may beconducted by immersing the inorganic phosphor particle in a metalcomplex solution, a metal alkoxide solution or a colloidal solution,followed by a heat treatment. According to this method, a light-emittingelement having a configuration facilitating the efficient generation ofthe discharge can be produced.

The covering with the insulative inorganic substance may be conducted byattaching the insulative inorganic substance on a surface of theinorganic phosphor particle by any one method of evaporation, sputteringand CVD. According to this method, a light-emitting element having aconfiguration facilitating the efficient generation of the discharge canbe produced.

Furthermore, after the second step and before the third step, a surfaceof the light-emitting body is covered with an insulative inorganicsubstance by immersing the light-emitting body in a metal complexsolution or a metal alkoxide solution, followed by a heat treatment.According to this method, a light-emitting element having aconfiguration facilitating the efficient generation of the discharge canbe produced.

Additionally, after the second step and before the third step, aninsulative inorganic substance may be attached to a surface of thelight-emitting body by any one method of evaporation, sputtering andCVD. According to this method, a light-emitting element having aconfiguration facilitating the efficient generation of the discharge canbe produced.

Furthermore, a display device can be produced by applying three types ofinorganic phosphor pastes including red, blue and green in a stripeform.

Furthermore, a light-shielding film or a groove may be provided betweendifferent colored inorganic phosphors. According to this method, alight-emitting element with distinctness and reduced spreading of colorscan be produced.

Furthermore, the inorganic phosphor paste may contain a foaming agent,which allows a light-emitting element having a porous configuration tobe produced easily.

In the second and the third methods for producing a light-emittingelement of the present invention, preferably, after the first step andbefore the second step, the light-emitting body is immersed in a metalcomplex solution, a metal alkoxide solution or a colloidal solution,followed by a heat treatment, whereby a surface of the inorganicphosphor particle is covered with an insulative inorganic substance.According to this method, a light-emitting element having aconfiguration facilitating the efficient generation of the discharge canbe produced.

Furthermore, by arranging the above-stated light-emitting elements ofthe present invention in a matrix form, a display device with a simpleconfiguration can be produced at a low cost.

The following are descriptions concerning specific embodiments.

Embodiment 1

The following describes Embodiment 1 that is directed to alight-emitting element of the present invention and a display deviceusing the same, with reference to the drawings.

FIG. 1 is a cross-sectional view of a light-emitting element 1 accordingto Embodiment 1 of the present invention, and FIGS. 2A and 2B arecross-sectional views of light-emitting particles constituting thelight-emitting element 1 shown in FIG. 1, where FIG. 2A shows a primaryparticle and FIG. 2B shows a secondary particle. Reference numeral 11denotes an inorganic phosphor particle that is a primary particle or aflocculated secondary particle, 12 denotes a coating layer made of MgOthat is an insulative metal oxide, 13 denotes a porous light-emittingbody made up of light-emitting particles 10 a and 10 b shown in FIG. 2Aand FIG. 2B, 14 a and 14 b denote ITO transparent electrodes that areprovided at surfaces of the light-emitting body 13 so as to have apredetermined gap therebetween and 1 denotes the light-emitting element.

The following describes a method for producing the light-emittingelement 1 of Embodiment 1. Firstly, Mg(OC₂H₅)₂ powder (1 molar ratio) asmetal alkoxide was mixed by stirring with CH₃COOH (10 molar ratio), H₂O(50 molar ratio) and C₂H₅OH (39 molar ratio) at room temperature,whereby a substantially transparent sol/gel solution was prepared. Next,inorganic phosphor powder (2 molar ratio) was mixed by stirring into thesol/gel solution. Thereafter, the mixed solution underwent centrifugalseparation so as to take powder only therefrom to a tray made ofstainless steel, which was allowed to dry at 150° C. all day and night.Next, the dried powder was calcined in the air at 400 to 600° C. for 2to 5 hours, so that light-emitting particles having a coating layer 12of MgO on a surface of the particles 11 (10 a (primary particle), 10 b(secondary particle)) (See FIG. 2) were manufactured. The light-emittingparticles 10 a and 10 b each were produced using, as the inorganicphosphor particles 11, three types of materials: BaMgAl₁₀O₁₇:Eu²⁺(blue); Zn₂SiO₄:Mn²⁺ (green); and YBO₃:Eu³⁺ (red), which had an averageparticle diameter of 2 to 3 μm. As a result of the observation with atransmission electron microscope (TEM), both of the light-emittingparticles 10 a and 10 b had thicknesses of the coating layer 12 from 0.1to 2.0 μm. Next, these light-emitting particles 10 a and 10 b were mixedwith 5 wt % polyvinyl alcohol and were granulated, followed by shapingthrough the application of a pressure at about 50 MPa into a disk shapewith a diameter of 10 mm and a thickness of 1 mm. Next, a heat treatmentwas conducted thereto in an atmosphere of nitrogen at 450 to 1200° C.for 2 to 5 hours, whereby a porous light-emitting body 13 was produced.Subsequently, indium tin oxide alloy (ITO) transparent electrodes 14 aand 14 b were formed by sputtering at upper and lower faces of thelight-emitting body 13, whereby a light-emitting element 1 was obtained.

A method for letting this light-emitting element 1 emit light will bedescribed below. Firstly, a voltage was applied between the electrodes14a and 14 b via lead wires 2 and 3. The voltage may be alternatingcurrent or direct current. The application of the voltage causes thegeneration of surface creepage at the coating layer 12. The dischargeoccurs continuously like a chain reaction, thus emitting ultravioletlight and visible light. Then, the thus generated ultraviolet lightoptically pumps the particles 11, thereby emitting visible light. Oncethe surface creepage begins, the discharge repeats like a chain reactionso as to generate ultraviolet light and visible light, and therefore inorder to suppress adverse effects of this light on the particles 10 aand 10 b, a value of the voltage preferably is reduced after theinitiation of the light-emission.

When the voltage was applied at about 0.5 to 1.0 kV/mm by means of an ACpower source or a DC power source, the surface creepage occurred,followed by the initiation of light-emission. A value of the current atthis time was 0.1 mA or smaller. Furthermore, once the light-emissionwas initiated, the light-emission continued even when the value of thevoltage was reduced to 50 to 80% of that applied at the initial state.It was confirmed that the light-emitting element had a high brightness,a high contrast, a high recognition capability and a high reliabilityfor all of the three colors: blue; green; and red. That is to say,although the light-emitting element 1 of Embodiment 1 has aconfiguration close to that of an inorganic EL, a light-emissionmechanism thereof is totally different. In Embodiment 1, the light(ultraviolet light) generated through the surface creepage by theapplication of the voltage pumps the particles 11, thus enablinglight-emission (photoluminescence). On the other hand, thelight-emission principle of the inorganic EL is as described in thesection of

BACKGROUND ART.

Therefore, although the phosphor used in the inorganic EL is asemiconductor light-emitting body typified by ZnS:Mn²⁺ and GaP:N, theparticles 11 of Embodiment 1 may be an insulator or a semiconductor.That is, even when a phosphor particle of a semiconductor is used, thelight-emission can continue without the generation of short-circuitbecause the particles are covered with the insulative metal oxideuniformly.

Furthermore, this light-emitting element 1 does not require vacuumencapsulation and a high voltage value that are required for the glowdischarge, and is expected to be a light-emitting element having a highbrightness, a high contrast, a high recognition capability and a highreliability in the air. Therefore, as compared with the organic EL andthe inorganic EL, this light-emitting element can have a simpleconfiguration and can be produced easily (does not require the use ofhigher level of thin-film technology). In addition, it was found thatefficient surface creepage significantly depended on a filling factor ofthe particles 10 a and 10 b. That is, since Embodiment 1 employs theporous light-emitting body 13, the surface creepage occurs not only atthe surface of the light-emitting body 13 but also at the insidethereof, whereby the particles 11 can emit light effectively. If adistance between the particles 10 a and 10 b that constitute thelight-emitting body 13 becomes too large, air discharge may occur, andtherefore care should be given to this point. Ideally, it is desirablefor the particles 10 a and 10 b to make point-contactthree-dimensionally with at least one adjacent particle 10 a or 10 b.

When a sintered density of the light-emitting body 13 is increased(e.g., 90% or higher of a theoretical density), the surface creepageoccurs only at the surface of the light-emitting body 13, thus degradingthe light-emission efficiency. Therefore, it is desirable that thelight-emission body 13 has a porous configuration with a density that is90% or less of the theoretical density. However, when pores of thelight-emitting body 13 become too large in size, which means anexcessively large porosity, the light-emission efficiency maydeteriorate, and moreover the surface creepage is expected to beunlikely to occur. Therefore, ideally, it appears appropriate that thelight-emitting body 13 has a sintered density of 50 to 90% of thetheoretical density. Herein, if a mechanical strength is providedtherewith, there is no need to apply a heat treatment for curing. It wasconfirmed that a shaped body (green compact) that was not subjected toany heat treatment also could emit light by the similar application of avoltage. Also, it was confirmed that a shaped body (green compact) withwhich polyvinyl alcohol had not been mixed could emit light similarly.

The coating layer 12 is formed as homogeneously and uniformly aspossible. As it becomes less homogeneous and uniform, although beingcapable of emitting light, a decrease in brightness and a deteriorationof life (deterioration due to ultraviolet light) become likely to occur.Furthermore, as a comparative example, a voltage was applied to alight-emitting body including the insulative particles 11 only and notincluding the coating layer 12 and its light-emission state wasevaluated. The surface creepage occurred at the surface of the inorganicphosphor particles and the light-emission similar to the presentembodiment was confirmed. However, the brightness instantly decreased,and it was difficult to emit light continuously.

From this, it was found that the coating layer 12 functioned not only togenerate the surface creepage and continue the discharge but also as aprotective film to suppress a deterioration due to ultraviolet light anda deterioration due to electric field of the particles 11.

Although the above-stated embodiment uses MgO as the coating layer 12,the reason for this is that a resistance value of MgO is as large as 10⁹Ω·cm or more, which allows the surface creepage to occur effectively. Inthe case of the resistance value below 10⁹ Ω·cm, the surface creepagebecomes unlikely to occur, and in the worst case a short-circuit mayoccur, and therefore such a value is not desirable. Thus, it isdesirable to use an insulative metal oxide with a resistance value of10⁹ Ω·cm or more. Herein, it is desirable not to use those havingproperties of shielding ultraviolet light anddeliquescence/efflorescence properties. Although most of these oxideshave properties of shielding ultraviolet light, such properties can beimproved by making a thickness of the coating thinner. Furthermore, theinsulative metal oxide constituting the coating layer 12 may be a stablesubstance having a considerably small standard free energy of formationof oxides ΔG_(f) ⁰(e.g., −100 kcal/mol or less at room temperatures) ormay be a substance having a capacity of 100 or more as a dielectricconstant. Thus, it is desirable that the insulative metal oxide alwayskeeps an insulative metal oxide property that tends not to be reducedeven when the surface creepage occurs, in addition to having a highinsulation resistance value.

Therefore, with consideration given to these matters, it is desirable toform the coating layer 12 using at least one of Y₂O₃, Li₂O, MgO, CaO,BaO, SrO, Al₂O₃, SiO₂, MgTiO₃, CaTiO₃, BaTiO₃, SrTiO₃, ZrO₂, TiO₂, B₂O₃,PbTiO₃,PbZrO₃ and PbZrTiO₃(PZT).

Furthermore, instead of the sol/gel method, the coating layer 12 may beformed by a chemical absorption method and a physical absorption methodusing a CVD method, a sputtering method, an evaporation method, a lasermethod, a shearing stress method and the like, from which the sameeffects as above can be obtained. It is important for the coating film12 to be formed homogeneously and uniformly so as not be peeled off.Thus, it is desirable, before the formation of the coating layer 12, toimmerse the inorganic phosphor particles 11 into a weak acid solutionsuch as acetic acid, oxalic acid and citric acid so as to washimpurities attached on a surface of the inorganic phosphor particles.This is because the coating layer 12 with a uniform thickness can beformed easily on the particles 11 whose surfaces have been washed.

Moreover, it is desirable to conduct pretreatment for the particles 11before the formation of the coating layer 12 in an atmosphere ofnitrogen at 200 to 500° C. for about 1 to 5 hours. The reason for thisis as follows: untreated particles 11 include a large amount of absorbedwater and water of crystallization, and when the coating layer 12 isformed on the particles 11 in such a state, a deterioration of lifeproperties such as a deterioration of brightness and a shift in emissionspectrum becomes remarkable. When the particles are washed with a weakacid solution, pretreatment may be conducted after the washing.

The points to note during the heat treatment process to form thelight-emitting body 13 include a temperature and an atmosphere where theheat treatment is conducted. In the above-stated embodiment, since theheat treatment is conducted in an atmosphere of nitrogen and atrelatively low temperatures (450 to 1200° C.), a valence of the dopedrare earth element in the particles 11 did not change. When thetreatment is conducted at higher temperatures, however, the valence ofthe doped rare earth element in the particles 11 may change or a solidsolution may form between the coating layer 12 and the particles 11, andtherefore care should be taken to avoid this. As a heat treatmenttemperature increases, a density of the light-emitting body 13increases, and therefore due care should be given thereto. Therefore, asthe ideal heat treatment temperatures, 450 to 1200° C. are preferable.As for the heat treatment atmosphere, it is desirable to conduct theheat treatment in an atmosphere of nitrogen with consideration given tothe valence of the doped rare earth element in the particles 11.

In the present embodiment, the thickness of the coating layer 12 is setat about 0.1 to 2.0 μm. However, the thickness may be determined withconsideration given to an average particle diameter of the particles 11and the efficiency of the surface creepage. Conceivably, the averageparticle diameter in a submicron order requires still thinner covering.A larger thickness of the coating layer 12 may result in a shift inemission spectrum, a deterioration of brightness and shielding ofultraviolet light, and therefore this is not preferable. Conversely, asmaller thickness of the coating layer 12 may result in the failure ofthe surface creepage. Therefore, a favorable relationship between theaverage particle diameter of the particles 11 and the thickness of thecoating layer 12 is the latter within 1/10 to 1/500 with reference tothe former assumed to be 1.

Furthermore, ideally, the light-emitting body 13 is constituted with theparticles 10 a that are the inorganic phosphor particle 11 as theprimary particles with the coating layer 12 made of the insulative metaloxide provided thereon as shown in FIG. 2A. Generally, however, it isconstituted with the light-emitting particles 10 b that are theflocculated particles with the coating layer 12 provided thereon asshown in FIG. 2B. As the light-emitting element, however, there is notmuch difference in performance between these light-emitting particles.

Furthermore, the electrodes 14 a and 14 b may be formed by attaching aglass on which an ITO film has been formed. If one of the electrodes istransparent, the other one may be a metal plate such as aluminum andstainless steel.

Embodiment 2

The following describes a light-emitting element 1 produced using porousinorganic phosphors, with reference to FIG. 3. FIG. 3 is across-sectional view of the light-emitting element 1 of Embodiment 2 ofthe present invention. Reference numeral 21 denotes a porous inorganicphosphor layer, 12 denotes a coating layer made of MgO that is aninsulative metal oxide, 23 denotes a porous light-emitting layer made upof the phosphor layer 21, the coating layer 12 and pores 16, 14 a and 14b denote ITO transparent electrodes that are provided at surfaces of thelight-emitting layer 23 so as to have a predetermined gap therebetween,1 denotes the light-emitting element and 15 denotes a through holeprovided in the light-emitting layer 23.

The following describes a method for producing the light-emittingelement 1 of Embodiment 2. Firstly, using the same three coloredinorganic phosphor powder as in Embodiment 1, each powder was mixed with5 wt % polyvinyl alcohol and was granulated, followed by shaping throughthe application of a pressure at about 50 MPa into a disk shape with adiameter of 10 mm and a thickness of 1 mm. During this step, throughholes 15 each having a diameter of 50 to 500 μm were bored at severalpoints randomly using a metal needle. Next, a heat treatment wasconducted thereto in an atmosphere of nitrogen at 450 to 1200° C. for 2to 5 hours, whereby a porous inorganic phosphor layer 21 was produced.Next, the phosphor layer 21 was immersed into a suspension, in whichMg(OH)₂ and ammonia water were mixed at substantially equal molarratios, for 10 to 30 minutes, which then was dried at 150° C. Thisimmersion and drying process was repeated several times. Thereafter, itwas calcined in the air at 400 to 600° C. for 2 to 5 hours, so that alight-emitting layer 23 was produced having a coating layer 12 of MgO ona surface of the phosphor layer 21 and having a myriad of pores 16.During this step, the coating layer 12 was formed on a surface of thethrough hole 15 and a surface of the pores 16 as well, which wasobserved with a transmission electron microscope (TEM). A thickness ofthe coating layer 12 was 0.1 to 2.0 μm. Subsequently, electrodes 14 aand 14 b were formed by sputtering at upper and lower faces of thelight-emitting layer 23, whereby a light-emitting element 1 wasobtained.

A method for letting this light-emitting element 1 emit light will bedescribed below. Similarly to Embodiment 1, a voltage was appliedbetween the electrodes 14 a and 14 b via lead wires 2 and 3. The voltagemay be alternating current or direct current. The application of thevoltage causes the generation of surface creepage at the coating layer12. The discharge occurs continuously like a chain reaction, thusemitting ultraviolet light and visible light. Then, the thus generatedultraviolet light optically pumps the phosphor layer 21, therebyemitting visible light. Once the surface creepage begins, the dischargerepeats like a chain reaction so as to generate ultraviolet light andvisible light, and therefore in order to suppress adverse effects ofthis light on the phosphor layer 23, a value of the voltage after theinitiation of the light-emission preferably is reduced to 50 to 80% ofthat applied at the initial state. When the voltage was applied at about0.3 to 1.0 kV/mm by means of an AC power source or a DC power source,the surface creepage occurred, followed by the initiation oflight-emission. A value of the current at this time was 0.1 mA orsmaller. Furthermore, once the light-emission was initiated, thelight-emission continued even when the value of the voltage was reduced.High-quality light-emission was confirmed similarly to Embodiment 1 forthe three colors of blue, green and red. The mechanism of thelight-emission is similar to that of Embodiment 1. In order to generatethe surface creepage effectively and obtain high-quality light-emission,the matters described in Embodiment 1 were executed, whereby favorableeffects could be attained.

Furthermore, in the present embodiment, the through holes 15 having adiameter of 50 to 500 μm were provided in the light-emitting layer 23 soas to improve the light-emission efficiency. In connection with this, ifthe through holes 15 are too large in size, air discharge may occur.Therefore care should be given to this point. Ideally, even when thethrough holes 15 are provided, it is desirable for the light-emittingparticles to make point-contact three-dimensionally with at least oneadjacent light-emitting particle. Thus, in order to suppress influencesof the air discharge and the mechanical strength, it is desirable tomake the diameter of the through holes 15 smaller than 2 mm.

The electrodes 14 a and 14 b may be formed by attaching a glass on whichan ITO film has been formed. If one of the electrodes is transparent,the other one may be a metal plate such as aluminum and stainless steel.

Embodiment 3

In the above Embodiment 2, the phosphor layer 21 is shaped using apressing machine. On the other hand, in the present embodiment, a pasteincluding light-emitting particles 10 a and 10 b is screen-printed so asto form a light-emitting element 1. The following describes such anembodiment, with reference to FIG. 4.

FIG. 4 is a cross-sectional view of the light-emitting element 1 ofEmbodiment 3 . Reference numeral 30 denotes a ceramic substrate, 33denotes a porous light-emitting body and 34 a and 34 b denote ITOtransparent electrodes. The light-emitting body 33 is an assembly of thelight-emitting particles 10 a and 10 b each including an inorganicphosphor particle 11 with a coating layer 12 made of MgO that is aninsulative metal oxide provided thereon.

The following describes a method for producing the light-emittingelement 1. Firstly, ethyl cellulose and α-terpineol were added to thelight-emitting particles 10 a and 10 b described in Embodiment 1 so asto prepare a paste. Next, the paste was screen-printed on a ceramicsubstrate 30, followed by drying. This process was repeated so as toproduce a thick layer of about 80 to 100 μm in printed thickness.Thereafter, a heat treatment was conducted in an atmosphere of nitrogenat 450 to 1200° C. for 2 to 5 hours, whereby a considerably porouslight-emitting body 33 was produced. The thickness of the light-emittingbody 33 at this step was about 50 to 80 μm. Thereafter, two ITOtransparent electrodes 34 a and 34 b were formed by sputtering on theupper surface of the light-emitting body 33. During this step, throughholes 15 having a diameter of 50 to 500 μm were provided randomly atseveral points using a metal needle. With this configuration, thelight-emitting element 1 shown in FIG. 4 was obtained. A method forletting this light-emitting element 1 emit light will be describedbelow. Similarly to Embodiments 1 and 2, a voltage was applied betweenthe electrodes 34 a and 34 b via lead wires 2 and 3. The voltage may bealternating current or direct current. The application of the voltagecauses the generation of an electric field across an arrow A. Thereby,surface creepage occurs at the coating layer 12, and the dischargeoccurs continuously like a chain reaction, thus emitting ultravioletlight and visible light. Then, the thus generated ultraviolet lightoptically pumps the particles 11, thereby emitting visible light. Oncethe surface creepage begins, the discharge repeats like a chain reactionso as to generate ultraviolet light and visible light, and therefore inorder to suppress adverse effects of this light on the light-emittingbody 33, a value of the voltage after the initiation of thelight-emission preferably is reduced to 50 to 80% of that applied at theinitial state. When the voltage was applied at about 0.1 to 0.8 kV/mm bymeans of an AC power source or a DC power source, the surface creepageoccurred, followed by the initiation of light-emission. A value of thecurrent at this time was 0.1 mA or smaller. Furthermore, once thelight-emission was initiated, the light-emission continued even when thevalue of the voltage was reduced. High-quality light-emission wasconfirmed similarly to Embodiments 1 and 2 for the three colors of blue,green and red.

The mechanism of the light-emission is similar to that of Embodiment 1.In order to generate the surface creepage effectively and obtainhigh-quality light-emission, the matters described in Embodiments 1 and2 were executed, whereby favorable effects could be attained.

Furthermore, according to Embodiment 3, the thickness of thelight-emitting body 33 could be made thinner than Embodiments 1 and 2,and the light-emission was confirmed even when the electrodes 34 a and34 b were formed on the same plane. Note here that, in the case wherethe electrodes 34 a and 34 b are formed on the same plane, a surfaceleakage may occur. Therefore, a distance between the electrodes 34 a and34 b should be controlled. Although the distance between the electrodes34 a and 34 b depends on the thickness of the light-emitting body 33 anda value of the voltage applied, at least 10 μm is required.

Herein, in Embodiment 3, available means for reducing a possibility ofthe surface leakage is to coat a surface of the light-emitting element 1with SiO₂ and the like. In this case, the SiO₂ on the electrodes 34 aand 34 b should be removed so as to allow electrical conduction.

Although the light-emitting element 1 of Embodiment 3 has aconfiguration close to that of an inorganic EL, a light-emissionmechanism thereof is totally different. The phosphor particles 11 ofEmbodiment 3 may be an insulator or a semiconductor. That is, even whena phosphor of a semiconductor is used, the light-emission can continuewithout the generation of short-circuit because the coating layer 12 isprovided.

In Embodiment 3, the paste including the light-emitting particles 10 aand 10 b is screen-printed, whereby the light-emitting element 1 wasformed.

The electrodes 34 a and 34 b may be formed by attaching a glass on whichan ITO film has been formed. Furthermore, the electrodes 34 a and 34 bmay be a metal plate such as aluminum and stainless steel instead oftransparent electrodes, because the light is emitted between theelectrodes 34 a and 34 b.

Embodiment 4

The following describes an embodiment in which a paste includingphosphor powder is screen-printed so as to form a light-emitting element1.

FIG. 5 is a cross-sectional view of the light-emitting element 1 ofEmbodiment 4 of the present invention. Reference numeral 21 denotes aporous inorganic phosphor layer, 12 denotes a coating layer made of MgOthat is an insulative metal oxide, 23 denotes a porous light-emittinglayer made up of the phosphor layer 21, the coating layer 12 and pores16, 34 a and 34 b denote ITO transparent electrodes provided at asurface of the light-emitting layer 23 so as to have a predetermined gaptherebetween, and 1 denotes the light-emitting element.

The following describes a method for producing the light-emittingelement 1 of Embodiment 4. Firstly, ethyl cellulose and α-terpineol wereadded to three-colored inorganic phosphor powder so as to prepare apaste. Next, the phosphor layer 21 was screen-printed on a ceramicsubstrate 30. The thickness of the phosphor layer 21 at this process wasabout 20 to 25 μm.

Thereafter, a heat treatment was conducted in an atmosphere of nitrogenat 450 to 1200° C. for 2 to 5 hours, whereby a porous phosphor layer 21having a large number of pores 16 in the layer was produced. A thicknessof the phosphor layer 21 at this step was about 15 to 20 μm.Additionally, MgO was formed by sputtering at an upper layer portion ofthe phosphor layer 21 so as to form a coating layer 12, whereby a porouslight-emitting layer 23 made up of the phosphor layer 21, the coatinglayer 12 and the pores 16 was formed. Thereafter, two ITO transparentelectrodes 34 a and 34 b were formed by sputtering on the upper surfaceof the light-emitting layer 23. With this configuration, thelight-emitting element 1 shown in FIG. 5 was obtained.

A method for letting this light-emitting element 1 emit light will bedescribed below. Similarly to the above-stated Embodiment 3 , a voltageis applied between the electrodes 34 a and 34 b via lead wires 2 and 3.The voltage may be alternating current or direct current. Theapplication of the voltage causes the generation of an electric fieldacross an arrow A. Thereby, surface creepage occurs at the coating layer12, and the discharge occurs continuously like a chain reaction, thusemitting ultraviolet light and visible light. Then, the thus generatedultraviolet light optically pumps the phosphor layer 21, therebyemitting visible light. Once the surface creepage begins, the dischargerepeats like a chain reaction so as to generate ultraviolet light andvisible light, and therefore in order to suppress adverse effects ofthis light on the light-emitting layer 23, a value of the voltage afterthe initiation of the light-emission preferably is reduced to 50 to 80%of that applied at the initial state. When the voltage was applied atabout 0.05 to 0.8 kV/mm by means of an AC power source or a DC powersource, the surface creepage occurred, followed by the initiation oflight-emission. A value of the current at this time was 0.1 mA orsmaller. Furthermore, once the light-emission was initiated, thelight-emission continued even when the value of the voltage was reduced.High-quality light-emission was confirmed similarly to Embodiments 1 to3 for the three colors of blue, green and red.

The mechanism of the light-emission is similar to that of Embodiment 2.In order to generate the surface creepage effectively and obtainhigh-quality light-emission, the matters described in Embodiments 1 and2 were executed, whereby favorable effects could be attained.

Furthermore, according to Embodiment 4, the thickness of thelight-emitting layer 23 could be made relatively thinner than the aboveEmbodiment 2, and the light-emission was confirmed even when theelectrodes 34 a and 34 b were formed on the same plane. Note here that,in the case where the electrodes 34 a and 34 b are formed on the sameplane, a surface leakage may occur. Therefore, a distance between theelectrodes 34 a and 34 b should be controlled. Although the distancebetween the electrodes 34 a and 34 b depends on the thickness of thelight-emitting layer 23 and a value of the voltage applied, at least 10μm is required.

Herein, in Embodiment 4, available means for reducing the possibility ofthe surface leakage include coating a surface of the light-emittingelement 1 with SiO₂ and the like. In this case, the SiO₂ on theelectrodes 34 a and 34 b should be removed so as to allow electricalconduction.

Although the light-emitting element 1 of Embodiment 4 has aconfiguration close to that of an inorganic EL, a light-emissionmechanism thereof is totally different. The phosphor layer 21 ofEmbodiment 4 may be an insulator or a semiconductor. That is, even whena phosphor of a semiconductor is used, the light-emission can continuewithout the generation of short-circuit because the coating layer 12 isprovided.

Furthermore, in Embodiment 4, it was confirmed that the provision of athrough hole 15 enabled light-emission at a lower voltage and even atthe inside of the phosphor layer 21. In the case where the thickness ofthe phosphor layer 21 was made thinner than 20 μm, it was confirmed thatthe light could be emitted sufficiently even at the inside of thephosphor layer 21 even in the absence of the through hole 15.

Moreover, since the MgO coating layer 12 formed by sputtering tends tobe an amorphous form, it is desirable to make this crystallized byconducting a heat treatment in an air or an atmosphere of nitrogen at450 to 1200° C. for 2 to 5 hours.

The electrodes 34 a and 34 b may be formed by attaching a glass on whichan ITO film has been formed. Furthermore, the electrodes 34 a and 34 bmay be a metal plate such as aluminum and stainless steel instead oftransparent electrodes, because the light is emitted between theelectrodes 34 a and 34 b.

Embodiment 5

FIG. 6 is a cross-sectional view of a light-emitting element 1 accordingto Embodiment 5 of the present invention. Reference numeral 11 denotesan inorganic phosphor particle that is a primary particle or aflocculated secondary particle, 12 denotes a coating layer made of MgOthat is an insulative metal oxide, 13 denotes a porous light-emittingbody made up of light-emitting particles 10 a and 10 b, 14 a and 14 bdenote ITO transparent electrodes that are provided at surfaces of thelight-emitting body 13 so as to have a predetermined gap therebetween,17 denotes a substance with low resistance and 1 denotes thelight-emitting element.

The following describes a method for producing the light-emittingelement 1 of Embodiment 5. Firstly, the light-emitting powder asproduced in Embodiment 1 (10 a [primary particle], 10 b[secondaryparticle]) (10 to 100 vol ratio), fine-grained metal powder (0.1 to 0.5μm) that contained at least one type among Pd, Pt, Ag, Ni, Cu and Zn (1vol ratio) and 5 wt % polyvinyl alcohol were mixed and granulized,followed by shaping through the application of a pressure at about 50MPa into a disk shape with a diameter of 10 mm and a thickness of 1 mm.Next, a heat treatment was conducted thereto in an atmosphere ofnitrogen or a reducing atmosphere at 450 to 1200° C. for 2 to 5 hours,whereby a porous light-emitting body 13 was produced. Subsequently, ITOtransparent electrodes 14 a and 14 b were formed by sputtering at upperand lower faces of the light-emitting body 13, whereby a light-emittingelement 1 was obtained. Lead wires 2 and 3 were connected thereto.Herein, the metal powder used in this step was Pd. Although thelight-emitting method was exactly the same as in Embodiment 1, adifference was in that the a value of the light-emission initiationvoltage was decreased to about 0.1 to 0.8 kV/mm. Although there is adifference depending on the resistance value and the amount of the metalpowder dispersed, it was confirmed that surface creepage occurred at alower voltage and high-quality light-emission was obtained similar toEmbodiment 1, and therefore practicality could be improved further.

Note here that the light-emission mechanism is the same as in Embodiment1.

Herein, in Embodiment 5, care should be taken for the control of theheat treatment temperature, its atmosphere and the particle diameter ofthe metal powder so as to prevent the metal powder 17 from generating asolid solution with the light-emitting particles 10 a and 10 b duringthe heat treatment process.

The reasons for selecting the above metal powder are as follows: thatis, Pd, Pt and Ag are metal materials that are resistant to oxidizingand are capable of holding low resistance values. Ni and Cu are metalmaterials that are susceptible to oxidizing, but they are capable ofholding a low resistance value during a heat treatment in the atmosphereand are at low cost. Furthermore, Zn assumes semiconductor propertieseven when it is oxidized and is capable of holding a relatively lowresistance value. Since these metal materials have different meltingpoints and some of them have melting points at 1000° C. or lower, careshould be taken for the heat treatment temperature. The particlediameter of the metal powder is 0.1 to 0.5 μm, which is finer than thelight-emitting body.

The electrodes 14 a and 14 b may be formed by attaching a glass on whichan ITO film has been formed. If one of the electrodes is transparent,the other one may be a metal plate such as aluminum and stainless steel.

Furthermore, instead of the metal powder, a low-resistant substancehaving flowability may be dispersed, whereby the similar effects can beobtained. This will be explained in Embodiment 6.

Embodiment 6

When the light-emitting element 1 produced in Embodiment 2 wasimpregnated with pure water, a weak acid solution such as oxalic acid,acetic acid, boric acid and citric acid or a conductive high polymersuch as polyacetylene for 10 to 30 minutes and the solution on a surfaceof the light-emitting element 1 was removed, followed by the applicationof a voltage, then the light-emission was initiated at a voltage valueof about 0.1 to 0.5 kV/mm. Surface creepage occurred at a lower voltageand it was confirmed that high-quality light-emission was obtainedsimilar to Embodiment 1.

In this step, if the conductive high polymer is dispersed in a matrixform, a short-circuit phenomenon occurs or the surface creepage becomesunlikely to occur. Therefore, in the case of the pure water and the weakacid solution being employed, drying at 50 to 80° C. for 5 to 10 minutesis required and in the case of the conductive high polymer, dilutionwith alcohol is required after the impregnation.

However, the sample of Embodiment 5 tends to dry by letting it stand inthe air or due to the heat generation during the surface creepage.Therefore, it is desirable to coat the light-emitting element 1 withSiO₂ or the like as shown in Embodiment 3 or to conduct vacuumencapsulation. In this case, the SiO₂ on the electrodes 14 a and 14 bwas removed so as to allow electrical conduction.

According to Embodiment 6, since the surface and the inside of thelight-emission body are impregnated with the conductive high polymer,there is a possibility that a short-circuit phenomenon occurs at theinitial stage of the application of the voltage. However, in a while,the light-emitting body generates heat and surface creepage occurstogether with the evaporation of moisture contents.

Embodiment 7

The following describes Embodiment 7 that is directed to alight-emitting element of the present invention and a display deviceusing the same, with reference to the drawings.

FIG. 7 is a cross-sectional view of a light-emitting element 1 ofEmbodiment 7 of the present invention, where reference numeral 11denotes an inorganic phosphor particle, 18 denotes a SiO₂—Al₂O₃—CaObased insulative fiber, 113 denotes a porous light-emitting body made upof the particle 11 and the insulative fiber 18, 14 denotes an ITOtransparent electrode and 40 denotes a metal substrate.

The following describes a method for producing the light-emittingelement 1 of Embodiment 7. As the inorganic phosphor particles 11, threetypes of particles including BaMgAl₁₀O_(17:Eu) ²⁺ (blue:B), Zn₂SiO₄:Mn²⁺(green:G) and Y₂O₃:Eu³⁺(red:R) were used, where the average particlediameter was 2 to 3 μm. For 100 g of each powder, 45 g of butyl acetate,10 g of BBP (butyl benzyl phthalate), 33.3 g of α-terpineol, 10 g ofthinner and 15 g of binder (butyral resin) were mixed so as to preparethree types of pastes. Next, these pastes were screen-printed on asheet-form sintered-body board made of SiO₂—Al₂O₃—CaO based insulativefibers 18, the board measuring 60 mm in length, 25 mm in width and about0.7 mm in thickness, where the pastes were separately applied like alateral stripe in the order of R, G and B. The width of the stripe was100 to 200 μm. The average particle diameter of the particles in thisstep was about 3 μm, and fibers with a diameter of about 10 to 20 μm anda length of 50 to 100 μm and fibers with a length of about 200 to 500 μmwere tangled in the board. Since a porosity (void ratio) of the board is50 to 90%, solvent of the printed paste immediately is absorbed into theinside. The particles 11 also enter into the board because the particlediameter is fine. The board assumes a clogged state gradually, and theparticles 11 that are prevented from entering are piled up onto thesurface of the board, thus resulting in the state shown in FIG. 7. Thatis, the particles 11 are present densely on one surface of the board.

If the diameter of the insulative fiber 18 is 20 μm or more and thelength of the same becomes larger than 100 μm, the surface of the boardbecomes coarse, so that it becomes difficult to apply the particles 11uniformly. Therefore, the preferable fiber diameter and the fiber lengthare 20 μm or less and 100 μm or less, respectively.

Herein the insulative fiber may include a needle-like particle, awhisker and moreover particles formed by crushing long fibers.

Next, this was dried in the air at 100 to 150° C., followed by a heattreatment conducted in the air or in an atmosphere of nitrogen at 450 to1200° C. for 0.25 to 10 hours, whereby a light-emitting body 113 wasproduced.

Thereafter, as a test specimen for confirming discharge, an indium tinoxide alloy (ITO) transparent electrode 14 was formed on an uppersurface of the light-emitting body 113 and a metal substrate 40 wasconnected to a lower surface of the light-emitting body 113, whereby alight-emitting element 1 was obtained. During this step, a contactproperty between the light-emitting body 113 and the electrodes 14 and40 was enhanced by using a colloidal silica aqueous solution or acolloidal alumina aqueous solution as an adhesive and drying it at 100to 200° C. As for the metal substrate 40, it was confirmed that the sameeffects could be obtained by baking an electrode paste to be attached.The lifetime was longer in the case using the colloidal silica aqueoussolution. The reason for this can be considered that the phosphorparticles are coated with colloidal particles, where the colloidalparticles function as a coating layer.

A method for letting this light-emitting element 1 emit light will bedescribed below. Firstly, a voltage was applied between the electrodes14 and 40 via lead wires 2 and 3. The voltage may be alternating currentor direct current. The application of the voltage causes the generationof discharge at a surface of the insulative fibers 18. The dischargeoccurs continuously like a chain reaction, thus emitting ultravioletlight and visible light. Then, the thus generated ultraviolet lightoptically pumps the particles 11, thereby emitting visible light.

Once the discharge begins, the discharge repeats like a chain reactionso as to generate ultraviolet light and visible light, and therefore inorder to suppress adverse effects of this light on the light-emittingbody 113, a value of the voltage preferably is reduced after theinitiation of the light-emission.

When the voltage was applied at about 0.3 to 1.0 kV/mm by means of an ACpower source or a DC power source, the discharge occurred, followed bythe initiation of light-emission. A value of the current at this timewas 0.1 mA or smaller. Furthermore, once the light-emission wasinitiated, the light-emission continued even when the value of thevoltage was reduced to 50 to 80% of that applied at the initial state.It was confirmed that the light-emitting element 1 had a highbrightness, a high contrast, a high recognition capability and a highreliability for all of the three colors: blue; green; and red.

Although the light-emitting element 1 of Embodiment 7 has aconfiguration close to that of an inorganic EL, the light-emissionmechanism thereof is totally different. More specifically, the light(ultraviolet light) generated through the discharge by the applicationof the voltage pumps the inorganic phosphor particle 11, thus enablinglight-emission (photoluminescence). On the other hand, thelight-emission principle of the inorganic EL is as described in thesection of BACKGROUND ART.

Furthermore, this light-emitting element 1 does not require vacuumencapsulation and a high voltage value that are required for the glowdischarge, and is expected to be a light-emitting element having a highbrightness, a high contrast, a high recognition capability and a highreliability in the air. Therefore, as compared with the organic EL andthe inorganic EL, this light-emitting element can have a simpleconfiguration and can be produced easily, which means that it does notrequire the use of higher level of thin-film technology.

In addition, it was found that efficient discharge significantlydepended on the porosity of the board made of the insulative fibers 18.That is, the discharge is unlikely to occur in a dense board with asmall porosity, and even when the discharge occurs, the light-emissionoccurs at the surface only, which results in a low light-emissionefficiency. That is, in order to emit light effectively, thelight-emitting body 113 needs to have a configuration that allows theparticles 11 to enter into the inside of the board. By making thelight-emitting body 113 porous as in Embodiment 7, the discharge occursnot only at the surface of the light-emitting body 113 but also at theinside thereof, so that the inorganic phosphor particles 11 emit lightefficiently.

Furthermore, it was found that plural insulative fibers 18 constitutingthe light-emitting body 113 overlapped so as to be a networkconfiguration, which became an important factor for the generation ofthe discharge.

Conversely, if the porosity of the board increases, smoothness of theboard surface is degraded, or a mechanical strength thereof becomes weakand brittle. Therefore, the preferable porosity of the board is 50 to90%.

Furthermore, the reasons for selecting SiO₂—Al₂O₃—CaO based fibers asthe insulative fibers 18 are as follows: these fibers are thermally andchemically stable and have a resistance value of 10⁹ Ω·cm or more, andcan have a configuration that enables a large porosity of 50 to 90%.Therefore, the discharge occurs at a surface of each fiber, resulting inthe discharge generated at the board as a whole. When the board is toodense, the discharge occurs only at the surface or at the end portionthereof. Note here that the use of a sintered-body board containing SiC,ZnO, TiO2, MgO, BN or Si₃N₄ based fiber can produce the similar effects.

Additionally, another important point is the heat treatment condition.The heat treatment temperature and its atmosphere should be controlleddepending on the composition of the fibers so as to prevent the fibersand the inorganic phosphor particles 11 from reacting with each otherand generating a solid solution therebetween during the heat treatmentprocess. In the present embodiment, the heat treatment was conducted inthe air or in the atmosphere of nitrogen for 0.25 to 10 hours, where thetemperature was set at a minimum temperature that allows the removal ofthe organic substances contained in the particles 11, i.e., at 450 to1200° C. If a large amount of organic substances is contained within thelight-emitting body 113, the deterioration of the light-emissionproperties and the life property becomes remarkable, and therefore careshould be taken to avoid this. However, if the organic binder is notused, there is no need to conduct the above-stated heat treatment. Forinstance, the board of the insulative fibers 18 is immersed in a slurryin which a colloidal silica aqueous solution is mixed with the phosphorparticles 11, which is then dried in the air at 100 to 200° C., wherebya porous light-emitting body 113 can be formed.

In the above-stated embodiment, a light-shielding film or a groove maybe provided between the respective colored inorganic phosphor regions ofR, G and B. For instance, as shown in FIG. 16A, a light-shielding film20 extending from a surface side toward the inside may be formed. Thelight-shielding film can be formed by coating with a black paste so thatthe paste coating can be absorbed through the surface of thelight-emitting body 113. A preferable width of the light-shielding film20 is 25 to 50 μm and a preferable depth of the same is 10 μm or more.

Furthermore, as shown in FIG. 16B, a groove 21 may be formed. Byproviding the light-shielding film or the groove, the mixture of thecolors of light emitted from the respective phosphors can be prevented,thus enabling a sharp full-colored display. A preferable width of thegroove 22 is 25 to 50 μm and a preferable depth of the same is 10 μm ormore.

Embodiment 8

Referring now to FIG. 8, an embodiment in which a surface of aninorganic phosphor particle is coated with an insulative inorganicsubstance will be described below.

FIG. 8 is a cross-sectional view of a light-emitting element 1 ofEmbodiment 8 of the present invention, where reference numeral 11denotes an inorganic phosphor particle, 12 denotes a coating layer, 18denotes a SiO₂—Al₂O₃—CaO based insulative fiber, 123 denotes a porouslight-emitting body made up of the particle 11 and the fiber 18, 14denotes an ITO transparent electrode, 40 denotes a metal substrate and 1denotes the light-emitting element.

The following describes a method for producing the light-emittingelement 1 of Embodiment 8. Firstly, a paste was prepared using the samethree-colored inorganic phosphor powder as in Embodiment 7. Next, thepaste was screen-printed on a sheet-form sintered-body board made of theSiO₂—Al₂O₃—CaO based insulative fibers 18 that measured about 0.7 mm inthickness.

Next, this was dried in the air at 100 to 150° C., followed by a heattreatment conducted in the air or in an atmosphere of nitrogen at 450 to1200° C. for 0.25 to 10 hours. Next, this was immersed in atetraethylorthosilicate (TEOS) solution (containing ethanol as asolvent, and concentration of 50 to 100%) at room temperature, which wasdried, followed by a heat treatment in the air or in an atmosphere ofnitrogen at 450 to 1200° C. for 0.25 to 1 hour, whereby a porouslight-emitting body 123 was produced in which the coating layer 12 wasformed on a surface of the inorganic phosphor particles 11 and theinsulative fibers 18. Subsequently, an ITO transparent electrode 14 anda metal substrate 40 were connected on upper and lower surfaces of thelight-emitting body 123, respectively, whereby a light-emitting element1 was obtained. During this step, a contact property between thelight-emitting body 123 and the electrodes 14 and 40 was enhanced byusing a colloidal silica aqueous solution or a colloidal alumina aqueoussolution as an adhesive and drying it at 100 to 200° C. As for the metalsubstrate 40, it was confirmed that the same effects could be obtainedby baking an electrode paste to be attached.

A method for letting this light-emitting element 1 emit light will bedescribed below. Similarly to Embodiment 7, a voltage was appliedbetween the electrodes 14 and 40 via lead wires 2 and 3. The voltage maybe alternating current or direct current. The application of the voltagecauses the generation of discharge at a surface of the coating layer 12.The discharge occurs continuously like a chain reaction, thus emittingultraviolet light and visible light. Then, the thus generatedultraviolet light optically pumps the particles 11, thereby emittingvisible light. Once the discharge begins, the discharge repeats like achain reaction so as to generate ultraviolet light and visible light,and therefore in order to suppress adverse effects of this light on thelight-emitting body 123, a value of the voltage preferably is reducedafter the initiation of the light-emission. When the voltage was appliedat about 0.3 to 1.0 kV/mm by means of an AC power source or a DC powersource, the discharge occurred, followed by the initiation oflight-emission. A value of the current at this time was 0.1 mA orsmaller. Furthermore, once the light-emission was initiated, thelight-emission continued even when the value of the voltage was reduced.It was confirmed that the high-quality light was emitted for threecolors of blue, green and red similar to Embodiment 7.

The mechanism of the light-emission is similar to that of Embodiment 7.In order to generate the discharge effectively and obtain high-qualitylight-emission, the matters described in Embodiment 7 were executed,whereby favorable effects could be attained.

The coating layer 12 was formed as homogeneously and uniformly aspossible. As it becomes less homogeneous and uniform, although beingcapable of emitting light, a decrease in brightness and a deteriorationof life (deterioration due to ultraviolet light) become likely to occur.The purpose of the coating layer 12 is to protect the particles 11 fromthe deterioration due to ultraviolet light and the deterioration due towater contents as well as to emit light effectively. As the dischargeoccurs, the light-emission efficiency becomes better. Although athickness of the coating layer 12 is set at 0.05 to 2.0 μm in thepresent embodiment, this may be determined with consideration given tothe average particle diameter of the particles 11 and a fiber diameterof the insulative fibers 18.

A larger thickness of the coating layer 12 may result in a shift inemission spectrum, a deterioration of brightness and shielding ofultraviolet light, and therefore this is not preferable. Therefore, afavorable relationship between the average particle diameter of theparticles 11 and the thickness of the coating layer 12 is the latterwithin 1/10 to 1/500 with reference to the former assumed to be 1.

In the present embodiment, SiO₂ is used as the coating layer 12. Thereason for this is that SiO₂ has a favorable film-formation property andeffects for preventing the deterioration due to ultraviolet light andthe deterioration due to water contents of the particles 11, which isthe main purpose thereof.

In addition to the above-described effects, there are other effects ofhaving a resistance value of 10⁹ Ω·cm or more and allowing the dischargeto occur effectively. In the case of the resistance value below 10⁹Ω·cm, the discharge becomes unlikely to occur, and in the worst case,short-circuit may occur, and therefore such a value is not desirable.Thus, it is desirable to form the coating layer 12 using an insulativemetal oxide with a resistance value of 10⁹ Ω·cm or more. Herein, it isdesirable not to use those having properties of shielding ultravioletlight and water-absorption/deliquescence/efflorescence properties.Although most of the insulative metal oxides have properties ofshielding ultraviolet light, such properties can be improved by makingthe thickness of the coating thinner.

Furthermore, the insulative metal oxide constituting the coating layer12 may be a stable substance having a considerably small standard freeenergy of formation of oxide ΔG_(f) ⁰ (e.g., −100 kcal/mol or less atroom temperatures) or may be a substance having a capacity of 100 ormore as a dielectric constant. Thus, it is desirable that the insulativemetal oxide always keeps an insulative metal oxide property that tendsnot to be reduced even when the discharge occurs, in addition to havinga high insulation resistance value.

Therefore, with consideration given to these matters, it is desirable toform the coating layer 12 using at least one of Y₂O₃, Li₂O, MgO, CaO,BaO, SrO, Al₂O₃, SiO₂, MgTiO₃, CaTiO₃, BaTiO₃, SrTiO₃, ZrO₂, TiO₂, B₂O₃,PbTiO₃, PbZrO₃ and PbZrTiO₃ (PZT).

Furthermore, instead of the sol/gel method, the coating layer 12 may beformed by a chemical absorption method, a physical absorption methodsuch as a CVD method, a sputtering method, an evaporation method, alaser method, a shearing stress method and the like, from which the sameeffects as above can be obtained. It is important for the coating film12 to be formed as homogeneously and uniformly as possible so as not bepeeled off. Thus, it is desirable to, before the formation of thecoating layer 12, immerse the light-emitting body 123 into a weak acidsolution such as acetic acid, oxalic acid and citric acid so as to washimpurities attached on a surface of the light-emitting body. This isbecause the coating layer 12 with a uniform thickness can be formedeasily on the light-emitting body 123 whose surfaces have been washed.

The points to note during the two heat treatment processes to form thelight-emitting body 123 include a temperature and an atmosphere wherethe heat treatment is conducted. In the present embodiment, since theheat treatment is conducted in the air or in an atmosphere of nitrogenand at relatively low temperatures, a valence of the doped rare earthelement in the inorganic phosphor particles 11 did not change. When thetreatment is conducted at higher temperatures, however, the valence ofthe doped rare earth element may change or a solid solution may formbetween the coating layer 12 and the particles 11, and therefore careshould be taken to avoid this.

Therefore, care should be taken so as not to change the valence of therare earth element due to the heat treatment.

Furthermore, the phosphors used in Embodiment 8 may be a semiconductoror an insulator. Although the phosphor used in the inorganic EL is asemiconductor light-emitting body typified by ZnS:Mn²⁺ and GaP:N, theparticles 11 used in Embodiment 8 may be an insulator or asemiconductor. That is, even when a phosphor particle of a semiconductoris used, the light-emission can continue without the generation ofshort-circuit because the particles are covered with the coating layer12 made of the insulative metal oxide uniformly. As in Embodiment 7, theimmersion in a colloidal silica aqueous solution, followed by drying inthe air at 100 to 200° C. results in the formation of the coating layer12 on the surface of the inorganic phosphor particles 11 and theinsulative fibers 18. It was confirmed that the use of this coatinglayer 12 could produce the similar effects as well.

Embodiment 9

In Embodiments 7 and 8, an inorganic phosphor paste is applied to asheet-form sintered-body board made of insulative fibers and a heattreatment is conducted thereto, whereby a porous light-emitting body canbe produced. The following describes a method for producing alight-emitting body from a mixed powder of insulative fibers andinorganic phosphors.

Referring now to FIG. 9, a light-emitting element 1 that is producedusing a paste in which inorganic phosphor particles 11 and insulativefibers 18 are mixed will be described below. FIG. 9 is a cross-sectionalview of a light-emitting element 1 of Embodiment 9 of the presentinvention, where reference numeral 11 denotes an inorganic phosphorparticle, 12 denotes a coating layer, 18 denotes a SiO₂—Al₂O₃—CaO basedinsulative fiber, 133 denotes a porous light-emitting body made up ofthe particle 11 and the insulative fiber 18, 14 denotes an ITOtransparent electrode, 40 denotes a metal substrate and 1 denotes thelight-emitting element.

The following describes a method for producing the light-emittingelement 1 of Embodiment 9. Firstly, using the same three-coloredinorganic phosphor powder as in Embodiments 7 and 8, 1/10 to 10 weightpercentage of fiber powder was mixed with the inorganic phosphor powderassuming as 1, whereby mixture powder was prepared. Next, ethylcellulose and an organic solution such as a-terpineol or butyl acetatewere added thereto and pastes were produced using a kneader such as athree-roll type. The fibers 18 used in this step had a diameter of about1 to 2 μm and a length of about 25 to 50 μm. Next, the above pastes werescreen-printed on a Pt metal substrate 40, which was dried in the air at100 to 150° C., followed by a heat treatment conducted in the air or inan atmosphere of nitrogen at 450 to 1200° C. for 0.25 to 10 hours,whereby a porous light-emitting body 133 made up of the particles 11 andthe insulative fibers 18 was obtained. In this step, the applicationthickness after the heat treatment was 10 to 500 μm. Herein, smoothnessof the printed surface becomes worse by mixing with the insulativefibers 18. Thus, preferably, the inorganic phosphor powder and theinsulative fibers 18 are mixed and crushed with a ball mill and the likebeforehand and then a paste is produced so as to enhance the smoothness.Next, this was immersed in a tetraethylorthosilicate (TEOS) solution,which was dried, followed by a heat treatment in the air at 450 to 1200°C. for 0.25 to 10 hours, whereby a light-emitting body 133 was producedin which the SiO₂ coating layer 12 was formed on a surface of theinorganic phosphor particles 11 and the insulative fibers 18.Subsequently, an ITO transparent electrode 14 was connected on an uppersurface of the light-emitting body 133, whereby a light-emitting element1 was obtained. During this step, a contact property between thelight-emitting body 133 and the electrode 14 was enhanced by using acolloidal silica aqueous solution or a colloidal alumina aqueoussolution as an adhesive and drying it at 100 to 200° C.

A method for letting this light-emitting element 1 emit light will bedescribed below. Similarly to Embodiments 7 and 8, a voltage was appliedbetween the electrodes 14 and 40 via lead wires 2 and 3. The voltage maybe alternating current or direct current. The application of the voltagecauses the generation of discharge at a surface of the coating layer 12.The discharge occurs continuously like a chain reaction, thus emittingultraviolet light and visible light.

Then, the thus generated ultraviolet light optically pumps the particles11, thereby emitting visible light. Once the discharge begins, thedischarge repeats like a chain reaction so as to generate ultravioletlight and visible light, and therefore in order to suppress adverseeffects of this light on the light-emitting body 133, a value of thevoltage after the initiation of the light-emission preferably is reducedto 50 to 80% at the initial state. When the voltage was applied at about0.3 to 1.0 kV/mm by means of an AC power source or a DC power source,the discharge occurred, followed by the initiation of light-emission. Avalue of the current at this time was 0.1 mA or smaller. Furthermore,once the light-emission was initiated, the light-emission continued evenwhen the value of the voltage was reduced. It was confirmed that thehigh-quality light was emitted for three colors of blue, green and redsimilar to Embodiments 7 and 8.

The mechanism of the light-emission is similar to that of Embodiments 7and 8. In order to generate the discharge effectively and obtainhigh-quality light-emission, the matters described in Embodiments 7 and8 were executed, whereby favorable effects could be attained.

Furthermore, in the present embodiment, the light-emitting body 133 isformed using a paste of a mixture of the particles 11 and the insulativefibers 18, and therefore a concentration gradient in a depth directionof the particles 11 can be suppressed as compared with Embodiments 7 and8, and the light-emitting body 133 could emit light uniformly as awhole.

Moreover, as for the mixture ratio of the particles 11 with theinsulative fibers 18, as the amount of the former powder increases, theconfiguration becomes dense and the discharge becomes unlikely to occur.Conversely, as the amount of the latter powder increases, it has aporous configuration but the brightness thereof tends to deteriorate.Therefore, the mixture ratio should be the insulative fibers 18 being1/10 to 10 with reference to the particles 11 in terms of weightpercentage, which is preferably 1/5 to 5.

Furthermore, the insulative fibers 18 allow the discharge to begenerated in a network form. Therefore, the insulative fibers 18 shouldbe as fine as possible with consideration given to the configuration ofthe light-emitting body 133 and the light-emission intensity. Althoughthe SiO₂—Al₂O₃—CaO based fibers that were used as the currentlyavailable on the market had a diameter of about 1 to 2 μm and a lengthof about 25 to 50 μm, the length of the fibers can be short bymechanically crushing (about 5 μm) for the use. In the case of thefibers becoming too short, however, it becomes difficult to form anetwork, which results in difficulty in the generation of the discharge.Therefore, preferably, the diameter of the fibers is made up to about0.5 μm and the length of the fibers is made up to about 3 μm.

Furthermore, although the application thickness of the light-emittingbody 133 is 10 to 500 μm after the heat treatment, screen-printingrequires at least 5 μm of application thickness because, in the case ofthe thickness being too small, a short-circuit may occur during theapplication of a voltage. The optimum application thickness was 10 to100 μm. However, when the film is formed by evaporation, sputtering, aCVD method and the like, the thickness can be made smaller.

The coating layer 12 is formed as homogeneously and uniformly aspossible. As it becomes less homogeneous and uniform, although beingcapable of emitting light, a decrease in brightness and a deteriorationof life (deterioration due to ultraviolet light) become likely to occur.The purpose of this coating layer 12 is to protect the particles 11 fromthe deterioration due to ultraviolet light and the deterioration due towater contents as well as to emit light effectively. As the dischargeoccurs, the light-emission efficiency is improved remarkably. Although athickness of the coating layer 12 is set at about 0.05 to 2.0 μm in thepresent embodiment, this may be determined with a consideration given tothe average particle diameter of the particles 11 and a fiber diameterof the insulative fibers 18. A larger thickness of the coating layer 12may result in a shift in emission spectrum, a deterioration ofbrightness and shielding of ultraviolet light, and therefore this is notpreferable. Therefore, a favorable relationship between the averageparticle diameter of the particles 11 and the thickness of the coatinglayer 12 is the latter within 1/10 to 1/500 with reference to the formerassumed to be 1.

As in the above-stated embodiment, the coating layer 12 can be formed onthe surface of the inorganic phosphor particles 11 and the insulativefibers 18 by the immersion in a colloidal silica aqueous solutioninstead of a TEOS solution, which is dried in the air at 100 to 200° C.It was confirmed that the similar effects could be obtained from thiscoating layer 12 also.

In Embodiment 9, the coating layer 12 is formed. However, even in theabsence of the coating layer 12, the light-emitting body 133 can emitlight because the fibers tangling like a network facilitate thedischarge. However, the deterioration due to discharge and thedeterioration due to ultraviolet light could be suppressed well when thecoating layer 12 was formed.

In Embodiment 9, the light-emitting body 133 was applied at an upperlayer portion of the Pt metal substrate 40 and a heat treatment wasconducted thereto. However, the light-emitting body 133 may be appliedon a PET film, for instance, the PET film may be peeled off and a heattreatment may be conducted, and then a metal substrate 40 may beattached thereto. Herein, as an adhesive for this step, a colloidalsilica aqueous solution or a colloidal alumina aqueous solution wasused, which was dried at 100 to 200° C., whereby a contact strengthcould be increased. The metal substrate 40 used in this step may benoble metals other than Pt or base metals.

Embodiment 10

The following describes an embodiment in which electrodes are formed onthe same plane, with reference to FIG. 10.

FIG. 10 is a cross-sectional view of a light-emitting element 1 ofEmbodiment 10 of the present invention, where reference numeral 11denotes an inorganic phosphor particle, 12 denotes a coating layer, 18denotes a SiO₂—Al₂O₃—CaO based insulative fiber, 133 denotes a porouslight-emitting body made up of the coated particle 11 and the coatedinsulative fiber 18, 34 a and 34 b denote ITO transparent electrodesthat are provided on a surface of the light-emitting body 133, 30denotes a substrate made of ceramic, glass, metal or the like and 1denotes the light-emitting element.

The following describes a method for producing the light-emittingelement 1 of Embodiment 10. Firstly, the same pastes as in Embodiment 9were used. Next, the above pastes were screen-printed on the substrate30, which was dried in the air at 100 to 150° C., followed by a heattreatment conducted in the air or in an atmosphere of nitrogen at 450 to1200° C. for 0.25 to 10 hours, whereby a porous light-emitting body 133made up of the inorganic phosphor particles 11 and the insulative fibers18 was obtained. In this step, the application thickness after the heattreatment was 10 to 500 μm. Next, this was immersed in a magnesiumcomplex solution, which was dried, followed by a heat treatment in theair at 450 to 600° C. for 0.25 to 1 hour, whereby a light-emitting body133 was produced in which the MgO coating layer 12 was formed on asurface of the particles 11 and the fibers 18. The reason for using thecomplex solution in this step is that the complex solution facilitatesthe formation of a uniform and thin coating layer 12 as compared with asol/gel solution. Subsequently, ITO transparent electrodes 34 a and 34 bwere formed by sputtering on an upper surface of the light-emitting body133, whereby a light-emitting element 1 was obtained.

The electrodes 34 a and 34 b may be formed by attaching a glass on whichan ITO film has been formed. Furthermore, the electrodes 34 a and 34 bmay be a metal plate such as aluminum and stainless steel instead oftransparent electrodes, because the light is emitted between theelectrodes 34 a and 34 b.

A method for letting this light-emitting element 1 emit light will bedescribed below. A voltage was applied between the electrodes 34 a and34 b via lead wires 2 and 3. The voltage may be alternating current ordirect current. In this step, an electric field is generated between theelectrodes 34 a and 34 b (an arrow A). The application of the voltagecauses the generation of the discharge at a surface of the coating layer12, and the discharge occurs continuously like a chain reaction, thusemitting ultraviolet light and visible light. Then, the thus generatedultraviolet light optically pumps the inorganic phosphor particles 11,thereby emitting visible light. Once the discharge begins, the dischargerepeats like a chain reaction so as to generate ultraviolet light andvisible light, and therefore in order to suppress adverse effects ofthis light on the light-emitting body 133, a value of the voltage afterthe initiation of the light-emission preferably is reduced to 50 to 80%of that applied at the initial state. When the voltage was applied atabout 0.3 to 1.0 kV/mm by means of an AC power source or a DC powersource, the discharge occurred, followed by the initiation oflight-emission. A value of the current at this time was 0.1 mA orsmaller. Furthermore, once the light-emission was initiated, thelight-emission continued even when the value of the voltage was reduced.High-quality light-emission was confirmed similarly to Embodiments 7 to9 for the three colors of blue, green and red. The mechanism of thelight-emission is similar to that of Embodiments 7 to 9. In order togenerate the discharge effectively and obtain high-qualitylight-emission, the matters described in Embodiments 7 to 9 wereexecuted, whereby favorable effects could be attained.

The effects and the purposes of the coating layer 12 are as described inEmbodiments 8 and 9.

In Embodiment 10, the light-emitting body 133 is formed using a paste ofa mixture of the inorganic phosphor particles 11 and the insulativefibers 18 containing a SiO₂—Al₂O₃—CaO based substance as a maincomponent, and therefore a concentration gradient in a depth directionof the particles 11 can be suppressed as compared with Embodiments 7 and8, and the light-emitting body 133 could emit light uniformly as awhole.

Moreover, as for the mixture of the particles 11 with the fibers 18, asthe amount of the former powder increases, the configuration becomesdense and the discharge becomes unlikely to occur. Conversely, as theamount of the latter powder increases, it has a porous configuration butbrightness thereof tends to deteriorate. Therefore, the mixture ratioshould be the fibers 18 being 1/10 to 10 with reference to the particles11 in terms of weight percentage, which is preferably in a range of ⅕ to5.

Furthermore, according to Embodiment 10, the thickness of thelight-emitting body 133 could be made thinner than Embodiment 9, and thelight-emission was confirmed even when the electrodes 34 a and 34 b wereformed on the same plane.

Note here that, in the case where the electrodes 34 a and 34 b areformed on the same plane, surface leakage may occur. Therefore, adistance between the electrodes 34 a and 34 b should be controlled.Although the distance between the electrodes 34 a and 34 b depends onthe thickness of the light-emitting body 133 and a value of the voltageapplied, at least 10 to 1000 μm is required, and a preferable thicknessis 50 to 500 μm.

Herein, in Embodiment 10, available means for reducing the possibilityof the surface leakage include providing the coating layer 12 on asurface of the light-emitting element 1. In this case, the coating layer12 on the electrodes 34 a and 34 b should be removed so as to allowelectrical conduction.

As in the above-stated embodiment, the coating layer 12 can be formed onthe surface of the inorganic phosphor particles 11 and the insulativefibers 18 by the immersion in a colloidal silica aqueous solutioninstead of a magnesium complex solution, which is dried in the air at100 to 200° C. It was confirmed that the similar effects could beobtained from this coating layer 12 also.

In Embodiment 10, the coating layer 12 is formed. However, even in theabsence of the coating layer 12, the light-emitting body 133 could emitlight because the fibers tangling like a network facilitated thedischarge. However, the deterioration due to discharge and thedeterioration due to ultraviolet light could be suppressed well when thecoating layer 12 was formed.

In Embodiment 10, the light-emitting body 133 was applied at an upperlayer portion of the substrate 30 and a heat treatment was conductedthereto. However, the light-emitting body 133 may be applied on a PETfilm, for instance, the PET film may be peeled off and a heat treatmentmay be conducted, and then a substrate 30 may be attached thereto.Herein, as an adhesive for this step, a colloidal silica aqueoussolution or a colloidal alumina aqueous solution was used, which wasdried at 100 to 200° C., whereby a contact strength could be increased.

Embodiment 11

In Embodiments 8 to 10, the coating layer 12 is attached to both of theinorganic phosphors 11 and the insulative fibers 18. The followingdescribes an embodiment in which the coating layer 12 is attached onlyto the particles 11, with reference to FIG. 11.

FIG. 11 is a cross-sectional view of a light-emitting element 1 ofEmbodiment 11 of the present invention, where reference numeral 11denotes an inorganic phosphor particle, 18 denotes an insulative fibercontaining a SiO₂—Al₂O₃—CaO based substance as a main component, 143denotes a porous light-emitting body made up of the particle 11 and thefiber 18, 34 a and 34 b denote ITO transparent electrodes that areprovided on a surface of the light-emitting body 143, 30 denotes asubstrate made of ceramic, glass, metal or the like and 1 denotes thelight-emitting element.

The following describes a method for producing the light-emittingelement 1 of Embodiment 11. Firstly, three-colored inorganic phosphorparticles 11 each was immersed in a magnesium complex solution, whichwas dried, followed by a heat treatment conducted in the air at 450 to600° C. for 0.25 to 1 hour. The resulting product was crushed, whereby aMgO coating layer 12 was formed on a surface of the inorganic phosphorparticles 11. Next, with respect to the particles 11 provided with thecoating layer 12, 1/10 to 10 weight percentage of insulative fibers 18were mixed, whereby a mixture powder was prepared. Furthermore, anorganic solution such as α-terpineol or butyl acetate was added theretoand pastes were produced using a kneader such as a three-roll type. Thefibers 18 used in this step had a diameter of about 1 to 2 μm and alength of about 25 to 50 μm. Next, the above pastes were screen-printedon a substrate 30, which was dried in the air at 100 to 150° C.,followed by a heat treatment conducted in the air or in an atmosphere ofnitrogen at 450 to 1200° C. for 0.25 to 10 hours, whereby a porouslight-emitting body 143 made up of the particles 11 provided with thecoating layer 12 and the insulative fibers 18 was obtained. In thisstep, the application thickness after the heat treatment was 10 to 500μm. Subsequently, ITO transparent electrodes 34 a and 34 b wereconnected on an upper surface of the light-emitting body 143, whereby alight-emitting element 1 was obtained. The electrodes 34 a and 34 b maybe a metal plate such as aluminum and stainless steel instead oftransparent electrodes, because the light is emitted between theelectrodes 34 a and 34 b.

A method for letting this light-emitting element 1 emit light will bedescribed below. Similarly to Embodiment 10, a voltage was appliedbetween the electrodes 34 a and 34 b via lead wires 2 and 3. The voltagemay be alternating current or direct current. In this step, an electricfield is generated between the electrodes 34 a and 34 b (an arrow A).The application of the voltage causes the generation of the discharge ata surface of the coating layer 12, and the discharge occurs continuouslylike a chain reaction, thus emitting ultraviolet light and visiblelight.

Then, the thus generated ultraviolet light optically pumps the particles11, thereby emitting visible light. Once the discharge begins, thedischarge repeats like a chain reaction so as to generate ultravioletlight and visible light, and therefore in order to suppress adverseeffects of this light on the light-emitting body 143, a value of thevoltage after the initiation of the light-emission preferably is reducedto 50 to 80% of that applied at the initial state. When the voltage wasapplied at about 0.3 to 1.0 kV/mm by means of an AC power source or a DCpower source, the discharge occurred, followed by the initiation oflight-emission. A value of the current at this time was 0.1 mA orsmaller. Furthermore, once the light-emission was initiated, thelight-emission continued even when the value of the voltage was reduced.High-quality light-emission was confirmed similarly to Embodiments 7 to10 for the three colors of blue, green and red.

The mechanism of the light-emission is similar to that of Embodiments 7to 10. In order to generate the discharge effectively and obtainhigh-quality light-emission, the matters described in Embodiments 7 to10 were executed, whereby favorable effects could be attained.

The effects and the purposes of the coating layer 12 are as described inEmbodiments 8 to 10.

In the present embodiment, the light-emitting body 143 is formed using apaste of a mixture of the particles 11 and the fibers 18, and thereforea concentration gradient in a depth direction of the particles 11 can besuppressed as compared with Embodiments 7 and 8, and the light-emittingbody 143 could emit light uniformly as a whole.

Moreover, as for the mixture of the particles 11 with the fibers 18, asthe amount of the former powder increases, the configuration becomesdense and the discharge becomes unlikely to occur. Conversely, as theamount of the latter powder increases, it has a porous configuration butbrightness thereof tends to deteriorate. Therefore, the mixture ratioshould be the fibers 18 being 1/10 to 10 with reference to the particles11 in terms of weight percentage, which is preferably in a range of ⅕ to5.

Furthermore, according to Embodiment 11, the thickness of thelight-emitting body 143 could be made thinner than Embodiment 9, and thelight-emission was confirmed even when the electrodes 34 a and 34 b wereformed on the same plane. Note here that, in the case where theelectrodes 34 a and 34 b are formed on the same plane, a surface leakagemay occur. Therefore, a distance between the electrodes 34 a and 34 bshould be controlled. Although the distance between the electrodes 34 aand 34 b depends on the thickness of the light-emitting body 143 and avalue of the voltage applied, at least 10 to 1000 μm is required, and apreferable thickness is 50 to 500 μm.

In Embodiment 11, the light-emission was initiated at a slightly smallervoltage value than Embodiment 10. The reason for this can be consideredthat the coating layer 12 with a large resistance value is not providedon the insulative fibers 18.

In Embodiment 10, the light-emitting body 143 was applied at an upperlayer portion of the substrate 30 and a heat treatment was conductedthereto. However, the light-emitting body 143 may be applied on a PETfilm, for instance, the PET film may be peeled off and a heat treatmentmay be conducted, and then a substrate may be attached thereto. Herein,as an adhesive for this step, a colloidal silica aqueous solution or acolloidal alumina aqueous solution was used, which was dried at 100 to200° C., whereby a contact strength could be increased.

The coating layer 12 may be formed by the immersion of the inorganicphosphor particles 11 in a colloidal silica aqueous solution instead ofa magnesium complex solution, which is dried in the air at 100 to 200°C. and is crushed. It was confirmed that this resulted in the formationof the coating layer 12 having the similar effects.

Embodiment 12

In Embodiment 11, the light-emitting element is produced using as a basethe inorganic phosphor powder or powder in which powder (fibers) ismixed with inorganic phosphor powder. In Embodiment 12, a light-emittingelement 1 produced by using a paste to which a foaming agent further isadded will be described, with reference to FIG. 12.

FIG. 12 is a cross-sectional view of a light-emitting element 1 ofEmbodiment 12 of the present invention, where reference numeral 11denotes an inorganic phosphor particle, 18 denotes an insulative fibercontaining a SiO₂—Al₂O₃—CaO based substance as a main component, 153denotes a porous light-emitting body made up of the particle 11 and thefiber 18, 34 a and 34 b denote ITO transparent electrodes that areprovided on a surface of the light-emitting body 153, 30 denotes asubstrate made of ceramic, glass, metal or the like and 1 denotes thelight-emitting element.

The following describes a method for producing the light-emittingelement 1 of Embodiment 12. Firstly, a 1 to 25 wt % of pyrolyticchemical foaming agent was added and mixed to the pastes used inEmbodiment 11. The chemical foaming agent used in this step was anorganic pyrolytic foaming agent such as an azo compound group, a nitrosocompound group and a hydrazine compound group or an inorganic pyrolyticfoaming agent such as a bicarbonate group and a carbonate group. Theaverage particle diameter of the foaming agent in this step was 5 to 10μm. Next, the pastes were screen-printed on a substrate 30, which wasdried in the air at 50 to 250° C. so as to let the pastes foam.Thereafter, a heat treatment was conducted in the air or in anatmosphere of nitrogen at 450 to 1200° C. for 0.25 to 10 hours, wherebya porous light-emitting body 153 made up of the particles 11 providedwith the coating layer 12 and the fibers 18 was obtained. Theapplication thickness after the heat treatment was 20 to 1000 μm. Inorder to suppress the deformation of the light-emitting body 153 due toabrupt thermal expansion of the foaming agent, the drying process wasconducted slowly from a room temperature. When chemical foaming agentsincrease in temperature at 150 to 250° C., they undergo thermaldecomposition so as to evolve gas such as nitrogen gas and carbonic acidgas, which results in thermal expansion of the light-emitting body 153.Therefore, as the foaming agent, an organic pyrolytic type preferably isused.

Subsequently, the light-emitting element 1 was produced using the samemethod as in Embodiment 11. The light-emission method and the mechanismof the light-emission also are the same as in Embodiment 11. That is tosay, a voltage was applied between the electrodes 34 a and 34 b via leadwires 2 and 3. The voltage may be alternating current or direct current.In this step, an electric field is generated between the electrodes 34 aand 34 b (an arrow A). The application of the voltage causes thegeneration of the discharge at a surface of the coating layer 12, andthe discharge occurs continuously like a chain reaction, thus emittingultraviolet light and visible light.

Then, the thus generated ultraviolet light optically pumps the inorganicphosphor particles 11, thereby emitting visible light. Once thedischarge begins, the discharge repeats like a chain reaction so as togenerate ultraviolet light and visible light.

The mixture of the foaming agent causes the expansion of the volume andfurther enhances the discharge efficiency. Therefore, the light-emissionby the light-emitting element 1 produced in Embodiment 12 was initiatedat a smaller voltage value than that in Embodiment 11 by about 10%.Also, since elasticity of the light-emitting element is increased ascompared with the light-emitting element produced in Embodiment 11, alight-emission initiation voltage value can be decreased, for example,by applying a pressure thereto. The mixture ratio of the foaming agentpreferably is 1 to 10 wt % with reference to the particles 11. In thecase of a mixture ratio larger than this, a mechanical strength maydeteriorate, and in extreme cases, the light-emission intensity wasdegraded.

Embodiment 13

In Embodiments 7 to 12, the light-emitting elements 1 are produced byapplying an inorganic phosphor paste on a surface of a porous body madeup of insulative fibers 18 or by applying a paste in which insulativefiber 18 and inorganic phosphor particles 18 are mixed. In Embodiment13, a light-emitting element 1 produced by sheet forming will bedescribed, with reference to FIG. 13.

FIG. 13 is a cross-sectional view of a light-emitting element 1 ofEmbodiment 13 of the present invention, where reference numeral 11denotes an inorganic phosphor particle, 18 denotes an insulative fibercontaining a SiO₂—Al₂O₃—CaO based substance as a main component, 163denotes a porous light-emitting body made up of the particle 11 and thefiber 18, 14 denotes an ITO transparent electrode that is provided on asurface of the light-emitting body 163, 40 denotes a metal substrate and1 denotes the light-emitting element.

The following describes a method for producing the light-emittingelement 1 of Embodiment 13.

Firstly, inorganic phosphor particles 11 and insulative fibers 18 weremixed at a weight ratio of 2:1. For 100 g of the mixed powder, 35 g ofbutyl acetate, 0.5 g of BBP, 16 g of butylcellosolve, 8 g of ethanol and12 g of butyral resin were mixed so as to prepare a slurry.

Next, using a sheet forming apparatus, this was shaped so as to have asheet thickness of about 25 μm. Thereafter, the sheet was laminated tobe two to ten layers by a laminating apparatus, and a thickness afterthe lamination was adjusted to be about 50 to 250 μm.

Next, a heat treatment was conducted in the air or in an atmosphere ofnitrogen at 450 to 1200° C. for 0.25 to 10 hours, whereby alight-emitting body 163 was produced. A thickness of the light-emittingbody 163 at this step was 45 to 250 μm.

Thereafter, an ITO transparent electrode 14 and a metal substrate 40were connected to upper and lower surfaces of the light-emitting body163, respectively, whereby a light-emitting element 1 was obtained.

Similarly to Embodiments 7 to 9, a voltage was applied between theelectrodes 14 and 40. The voltage may be alternating current or directcurrent. The application of the voltage causes the generation of thedischarge at a surface of the electrical insulative fibers 18, and thedischarge occurs continuously like a chain reaction, thus emittingultraviolet light and visible light.

Then, the thus generated ultraviolet light optically pumps the particles11, thereby emitting visible light. Once the discharge begins, thedischarge repeats like a chain reaction so as to generate ultravioletlight and visible light, and therefore in order to suppress adverseeffects of this light on the light-emitting body 163, a value of thevoltage after the initiation of the light-emission preferably is reducedto 50 to 80% of that applied at the initial state. When the voltage wasapplied at about 0.3 to 1.0 kV/mm by means of an AC power source or a DCpower source, the discharge occurred, followed by the initiation oflight-emission. A value of the current at this time was 0.1 mA orsmaller. Furthermore, once the light-emission was initiated, thelight-emission continued even when the value of the voltage was reduced.High-quality light-emission was confirmed similarly to Embodiment 7 forthe three colors of blue, green and red.

The mechanism of the light-emission is similar to that of Embodiments 7to 12. In order to generate the discharge effectively and obtainhigh-quality light-emission, the matters described in Embodiments 7 to12 were executed, whereby favorable effects could be attained.

In Embodiment 13, when connecting the light-emitting body 163 with theelectrode 14 and the metal substrate 40, a colloidal silica aqueoussolution or a colloidal alumina aqueous solution was used as anadhesive, which was dried at 100 to 200° C., whereby a contact strengthcould be increased. Furthermore, by the immersion in a colloidal silicaaqueous solution, followed by drying in the air at 100 to 200° C., theformation of the coating layer 12 was confirmed.

Furthermore, in Embodiment 13, the coating layer 12 was not provided.However, the same effects can be produced even when the coating layer 12is provided. However, the deterioration due to discharge and thedeterioration due to ultraviolet light could be suppressed well when thecoating layer 12 was formed.

Embodiment 14

In the above Embodiments 7 to 13, organic binders are used, andtherefore the manufacturing process requires a degreasing step and aheat treatment needs to be conducted in the air or in an atmosphere ofnitrogen at 450 to 1200° C. for 0.25 to 10 hours. Thus, a method forproducing a porous light-emitting body 173 by drying it in the air at100 to 200° C. using an aqueous binder will be described below.

The following is a description for such an embodiment, with reference toFIG. 14. Firstly, inorganic phosphor powder 11 and insulative fibers 18containing a SiO₂—Al₂O₃—CaO based substance as a main component weremixed at a weight ratio of 2:1. For 100 g of the mixed powder, a 5 wt %of colloidal silica aqueous solution or a 50 g of colloidal aluminaaqueous solution was mixed so as to prepare a slurry.

Next, the slurry was placed on an Al metal foil 41, and drying wascarried out by a drier at 100 to 200° C. for 0.25 to 10 hours, whereby alight-emitting body 173 with a thickness of about 25 to 1000 μm wasproduced. Thereafter, an ITO transparent electrode 14 was connected toan upper surface of the light-emitting body 173, whereby alight-emitting element 1 was obtained.

Similarly to Embodiment 13, a voltage was applied between the electrodes14 and 40 via lead wires 2 and 3. The voltage may be alternating currentor direct current. The application of the voltage causes the generationof the discharge at a surface of the insulative needle-like particles(fibers) 18, and the discharge occurs continuously like a chainreaction, thus emitting ultraviolet light and visible light.

Then, the thus generated ultraviolet light optically pumps the particles11, thereby emitting visible light. Once the discharge begins, thedischarge repeats like a chain reaction so as to generate ultravioletlight and visible light, and therefore in order to suppress adverseeffects of this light on the light-emitting body 173, a value of thevoltage after the initiation of the light-emission preferably is reducedto 50 to 80% of that applied at the initial state. When the voltage wasapplied at about 0.3 to 1.0 kV/mm by means of an AC power source or a DCpower source, the discharge occurred, followed by the initiation oflight-emission. A value of the current at this time was 0.1 mA orsmaller. Furthermore, once the light-emission was initiated, thelight-emission continued even when the value of the voltage was reduced.High-quality light-emission was confirmed similarly to Embodiment 7 forthe three colors of blue, green and red.

The mechanism of the light-emission is similar to that of Embodiment 13.In order to generate the discharge effectively and obtain high-qualitylight-emission, the matters described in Embodiment 13 were executed,whereby favorable effects could be attained.

As for this step, the light-emitting body 173 can be formed also byconducting a heat treatment in the air or in an atmosphere of nitrogenat 450 to 1200° C. for 0.25 to 10 hours, and the generation of the samelight-emission phenomenon was confirmed.

In Embodiment 14, the coating layer 12 was formed by the formation ofcolloidal particles on a surface of the inorganic phosphor particles 11and the insulative fibers 18. That is to say, it was confirmed that thecolloidal silica aqueous solution or the colloidal alumina aqueoussolution that was used as the binder also formed the coating layer 12.Note here that, as an organic binder, instead of the colloidal silicaaqueous solution or the colloidal alumina aqueous solution, polyimide,BCB (benzocyclobutene), a fluororesin such as PTFE(polytetrafluoroethylene) and a thermosetting resin or a thermoplasticresin such as aramid, PBO (poly-para-phenylene benzo-bis-oxazole),wholly aromatic polyester, epoxy resin, cyanate ester resin, phenolresole resin, PPE (poly-phenylene ether) resin, bismaleimide-triazineresin, unsaturated polyester resin, PPE (polyphenylene ether) resin,PEEK (poly-etheretherketone) resin and PEK (polyether-ketone) resin areavailable.

Embodiment 15

The following describes a method for producing a porous light-emittingbody 183 using a ZnO based whisker as an insulative needle-likeparticle, with reference to FIG. 15. Firstly, particles 11 and ZnOwhiskers 19 were mixed at a weight ratio of 2:1. For 100 g of the mixedpowder, a 5 wt % of colloidal silica aqueous solution or a 50 g ofcolloidal alumina aqueous solution was mixed so as to prepare a slurry.Next, the slurry was placed on a Cu metal foil 41, and drying wascarried out with a drier at 100 to 200° C. for 0.25 to 10 hours, wherebya light-emitting body 183 with a thickness of about 25 to 1000 μm wasproduced. Thereafter, an ITO transparent electrode 14 was connected toan upper surface of the light-emitting body 183, whereby alight-emitting element 1 was obtained.

Next, similarly to Embodiment 14, a voltage was applied between theelectrodes 14 and 40 via lead wires 2 and 3. The voltage may bealternating current or direct current. The application of the voltagecauses the generation of the discharge at a surface of the whiskers 19,and the discharge occurs continuously like a chain reaction, thusemitting ultraviolet light and visible light.

Then, the thus generated ultraviolet light optically pumps the particles11, thereby emitting visible light. Once the discharge begins, thedischarge repeats like a chain reaction so as to generate ultravioletlight and visible light, and therefore in order to suppress adverseeffects of this light on the light-emitting body 183, a value of thevoltage after the initiation of the light-emission preferably is reducedto 50 to 80% of that applied at the initial state. When the voltage wasapplied at about 0.3 to 1.0 kV/mm by means of an AC power source or a DCpower source, the discharge occurred, followed by the initiation oflight-emission. A value of the current at this time was 0.1 mA orsmaller. Furthermore, once the light-emission was initiated, thelight-emission continued even when the value of the voltage was reduced.High-quality light-emission was confirmed similarly to Embodiment 7 forthe three colors of blue, green and red.

The mechanism of the light-emission is similar to that of Embodiment 14.In order to generate the discharge effectively and obtain high-qualitylight-emission, the matters described in Embodiment 14 were executed,whereby favorable effects could be attained.

As for this step, the light-emitting body 183 can be formed also byconducting a heat treatment in the air or in an atmosphere of nitrogenat 450 to 1200° C. for 0.25 to 10 hours, and the generation of the samelight-emission phenomenon was confirmed.

In Embodiment 15, the coating layer 12 was formed by the formation ofcolloidal particles on a surface of the inorganic phosphor particles 11and the insulative fibers 18. That is to say, it was confirmed that thecolloidal silica aqueous solution or the colloidal alumina aqueoussolution that was used as the binder also formed the coating layer 12.

Furthermore, in the above embodiments, a porous configuration isrealized by using a SiO₂—Al₂O₃—CaO based insulative fiber, for example.However, the use of the ZnO whiskers facilitates the formation of athree-dimensional porous configuration, which further facilitates thegeneration of the discharge, thus resulting in enhancement of thelight-emission intensity.

Although Cu was used as the electrode substrate, its resistance valuewas low, which bore comparison with Al.

Embodiment 16

The light-emitting elements 1 produced in Embodiments 1 to 15 wereinserted in a quartz tube, which was then filled with inert gas such asNe, Ar, Kr and Xe gas. Thereafter, when a voltage was applied to thelight-emitting elements 1, light-emission was initiated at a voltagevalue of about 0.03 to 0.8 kV/mm. As compared with the case not filledwith inert gas, the light-emitting elements indicated the voltage valuedecreased by about 60 to 80% and a higher brightness, a higher contrast,a higher recognition capability and a higher reliability. The reason forthis is that the filling with the inert gas can provide an atmospherethat facilitates the generation of the discharge and the generation ofultraviolet light. In this case, however, glow discharge could beconfirmed.

The thus obtained light-emitting elements 1 of Embodiments 1 to 16 arearranged two-dimensionally in a matrix form and a voltage applied toeach of the light-emitting elements is turned ON or OFF by a drivingcircuit, whereby a flat display can be produced. With this flat display,a simple configuration can be realized at a low cost.

Although SiO₂—Al₂O₃—CaOO based compositions were used for the insulativefibers 18 in Embodiments 7 to 14, Al₂O₃, SiC, ZnO, TiO₂, MgO, BN, Si₃N₄based fibers can produce the same effects as well.

INDUSTRIAL APPLICABILITY

As is evident from the above descriptions, according to the presentinvention, a light-emitting element that is reduced in a deteriorationof brightness and a degradation of reliability of phosphors and does notrequire the vacuum encapsulation and the application of a high voltage,which are required for glow discharge, and still-higher level ofthin-film technology can be provided. By arranging these light-emittingelements two-dimensionally in a matrix form, a flat display device witha simple configuration can be provided.

1. A light-emitting element, comprising: a porous light-emitting bodyincluding an insulator having a void and an inorganic phosphor particle;and at least two electrodes provided so as to contact with a surface ofthe light-emitting body, wherein a voltage is applied to the at leasttwo electrodes so as to generate discharge, and the light-emitting bodyis pumped by the discharge so as to emit light.
 2. The light-emittingelement according to claim 1, wherein ultraviolet light is emitted bythe discharge.
 3. The light-emitting element according to claim 1,wherein a surface of the porous light-emitting body is formed of aninsulative inorganic substance.
 4. The light-emitting element accordingto claim 1, wherein the porous light-emitting body is formed of anassembly of inorganic phosphor particles whose surfaces are coated withan insulative inorganic substance.
 5. The light-emitting elementaccording to claim 3, wherein the insulative inorganic substance is atleast one substance selected from the group consisting of Y₂O₃, Li₂O,MgO, CaO, BaO, SrO, Al₂O₃, SiO₂, MgTiO₃, CaTiO₃, BaTiO₃, SrTiO₃, ZrO₂,TiO₂, B₂O₃, PbTiO₃, PbZrO₃ and PbZrTiO₃ (PZT).
 6. The light-emittingelement according to claim 1, wherein a through hole is provided in thelight-emitting body between the electrodes.
 7. The light-emittingelement according to claim 1, wherein a substance with resistance lowerthan that of an insulative metal oxide is dispersed within thelight-emitting body between the electrodes.
 8. The light-emittingelement according to claim 1, wherein an inside of the light-emittingbody is an atmosphere at atmospheric pressure or is filled with inertgas.
 9. The light-emitting element according to claim 1, wherein thedischarge is surface creepage.
 10. The light-emitting element accordingto claim 1, wherein the insulator having a void is at least one selectedfrom a fibrous structure and a foam having continuous bubbles.
 11. Thelight-emitting element according to claim 1, wherein the light-emittingbody is one obtained by attaching the inorganic phosphor particle to asurface of the insulator having a void.
 12. The light-emitting elementaccording to claim 1, wherein the insulator having a void is aninorganic substance that contains at least one type selected from thegroup consisting of Al, Si, Ca, Mg, Ti, Zn and B.
 13. The light-emittingelement according to claim 10, wherein the fiber is one obtained bycrushing insulative ceramic or glass.
 14. The light-emitting elementaccording to claim 10, wherein the fiber is a heat-resistant syntheticfiber with a heat distortion temperature of 220° C. or more.
 15. Thelight-emitting element according to claim 1, wherein a substance withresistance lower than that of the insulator is dispersed within thelight-emitting body.
 16. The light-emitting element according to claim1, wherein assuming that a weight of the insulator is 1, a weight of theinorganic phosphor particle is within a range of 0.1 to 10.0.
 17. Thelight-emitting element according to claim 10, wherein the fiber has adiameter of 0.1 to 20.0 μm and a length of 0.5 to 100 μm, and theinorganic phosphor particle has an average particle diameter of 0.1 to5.0 μm.
 18. The light-emitting element according to claim 1, wherein aporosity of the insulator having a void is within a range of 50% to 90%,inclusive.
 19. A display device in which the light-emitting elementsaccording to claim 1 are arranged in a matrix form.
 20. A method forproducing the light-emitting element according to claim 1, comprisingthe steps of: a first step of applying an inorganic phosphor paste on asurface of a sheet-form porous body made up of the insulator having avoid; a second step of conducting a heat treatment for the insulator soas to form the porous light-emitting body; and a third step of formingthe at least two electrodes contacting with the surface of thelight-emitting body.
 21. The method for producing the light-emittingelement according to claim 20, wherein the inorganic phosphor pastecontains an inorganic phosphor particle whose surface is covered with aninsulative inorganic substance.
 22. The method for producing thelight-emitting element according to claim 21, wherein the covering withthe insulative inorganic substance is conducted by immersing theinorganic phosphor particle in at least one solution selected from thegroup consisting of a metal complex solution, a metal alkoxide solutionand a colloidal solution, followed by a heat treatment.
 23. The methodfor producing the light-emitting element according to claim 21, whereinthe covering with the insulative inorganic substance is conducted byattaching the insulative inorganic substance on a surface of theinorganic phosphor particle by any one method of evaporation, sputteringand CVD.
 24. The method for producing the light-emitting elementaccording to claim 20, wherein after the second step and before thethird step, a surface of the light-emitting body is covered with aninsulative inorganic substance by immersing the light-emitting body inat least one solution selected from the group consisting of a metalcomplex solution, a metal alkoxide solution and a colloidal solution,followed by a heat treatment.
 25. The method for producing thelight-emitting element according to claim 20, wherein after the secondstep and before the third step, an insulative inorganic substance isattached to a surface of the light-emitting body by any one method ofevaporation, sputtering and CVD.
 26. The method for producing thelight-emitting element according to claim 20, wherein, in the firststep, three types of inorganic phosphor pastes including red, blue andgreen are applied in a stripe form.
 27. The method for producing thelight-emitting element according to claim 26, wherein a light-shieldingfilm or a groove is provided between different colored inorganicphosphors.
 28. The method for producing the light-emitting elementaccording to claim 20, wherein the inorganic phosphor paste contains afoaming agent.
 29. A method for producing the light-emitting elementaccording to claim 1, comprising the steps of: a first step of applyinga paste containing an insulative fiber and an inorganic phosphorparticle on a conductive substrate and conducting a heat treatment so asto form the porous light-emitting body, and a second step of forming theelectrodes so as to contact with the surface of the light-emitting body.30. A method for producing the light-emitting element according to claim1, comprising the steps of: a first step of shaping a paste containingan insulative fiber and an inorganic phosphor particle and conducting aheat treatment so as to form the porous light-emitting body, and asecond step of forming the at least two electrodes so as to contact withthe surface of the light-emitting body.
 31. The method for producing thelight-emitting element according to claim 29, wherein after the firststep and before the second step, the light-emitting body is immersed inat least one solution selected from the group consisting of a metalcomplex solution, a metal alkoxide solution and a colloidal solution,followed by a heat treatment, whereby a surface of the inorganicphosphor particle is covered with an insulative inorganic substance.